4.4.1 Diplomatic Relations

As is so often the case when seeking answers to legal questions, one can find landmark cases that shed an unexpected amount of light on a particular issue. This certainly holds true when it comes to the importance of CIL within the EU’s internal legal sphere, where the landmark case concerned the president of Hungary, who in 2009 was invited to a privately organized event in Slovakia (a ceremony inaugurating a statue of Saint Stephen, the founder and first King of Hungary). For Slovakia, the specific date of the planned inauguration was politically sensitive given that it marked the invasion of Czechoslovakia in 1968 by five Warsaw Pact countries, including Hungary. After Slovakia barred the Hungarian president from entering Slovak territory, the president cancelled the visit but the diplomatic row between the two countries festered and finally ended up before the CJEU as one of the few inter-state disputes over an infringement of EU law (Article 259 TFEU).

In Hungary v. Slovakia the CJEU held that the Slovak Republic’s decision to refuse entry to the president of Hungary did not violate EU law despite the president holding EU citizenship.Footnote ³¹ Most interestingly in the context of this present chapter, the CJEU did not reach this conclusion on the basis of the security exception within Directive 2004/38/EC,Footnote ³² but with reference to CIL and its legal relationship to Article 21 TFEU, namely the primary law provision on EU citizenship.

The justification for making primary law the starting point of all further legal considerations lies in the CJEU’s consistent case-law, as introduced in RackeFootnote ³³ and according to which CIL is a part of EU law and thus binding upon EU institutions.Footnote ³⁴ In the light of this tenet, in Hungary v. Slovakia the CJEU first concluded that in order to avoid normative conflicts with EU primary law, Article 21 TFEU had to be interpreted in the light of the relevant rules of CIL.Footnote ³⁵ The CJEU’s second conclusion was that this international-law friendly interpretation of Article 21 TFEU may result in an ‘unwritten’ limitation of the free movement of EU citizens on account of CIL.Footnote ³⁶ After having established the status of heads of state under CIL, reflected inter alia in their privileges, immunities and special protection, the CJEU had to decide next what status prevailed in the case at hand, that of head of state under CIL or that of an EU citizen under Article 21 TFEU. After considering the former’s status specialis and the latter’s status generalis, the CJEU concluded:

By allowing, within the scope of Article 21 TFEU, unwritten grounds of limitation which originate from an international legal source, that is, CIL, the CJEU has demonstrated an inclination to find a means to circumvent the express wording of Article 21(1) TFEU (‘subject to the limitations and conditions laid down in the treaties and by the measures adopted to give them effect’). As a side note, it is worth mentioning that the CJEU is not the only court that has acknowledged that implicit international law limitations extend to primary law. For example, the European Court of Human Rights (ECtHR) considers Article 6 European Convention on Human Rights (ECHR)Footnote ³⁸ (right to a fair trial) to be subject to limitations by ‘way of implication’Footnote ³⁹ and ruled on several occasions that the jurisdictional immunities of IOs and states, based on agreements and CIL, are legitimate limitations on that right.Footnote ⁴⁰

Hungary v. Slovakia attracted some scholarly attention as it was widely regarded as a judicial regressionFootnote ⁴¹ to a more monistic understanding of the relationship between EU law and international law. This is considered remarkable as the CJEU in KadiFootnote ⁴² famously detached EU law from the UN Charter in a rather dualistic fashion, with the declared aim of protecting the constitutional principles of the EU treaties from being undermined at international level.Footnote ⁴³

In contrast to its reasoning in Kadi, in Hungary v. Slovakia the CJEU did not dwell on the constitutional nature of EU citizenship as reflected in Article 45(1) Charter of Fundamental Rights of the European UnionFootnote ⁴⁴ (FRC), even though it reiterated Grzelczyk, in which the CJEU had authoritatively established that ‘Union citizenship is destined to be the fundamental status of nationals of the Member States’.Footnote ⁴⁵ Obviously, the CJEU was not concerned that the rules of CIL governing head-of-state visits undermine the fundamental status bestowed on EU citizens but argued exclusively on the basis of status specialis and status generalis considerations, which translates to CIL defining the legal status of the head of state being lex specialis and Article 21 TFEU defining the legal status of EU citizens being lex generalis.

This leads to the conclusion that in Hungary v. Slovakia the CJEU accepted that EU member states, when introducing the EU citizenship into primary law (Article 21 TFEU), had no intention to ‘contract out’ the customary rules governing their mutual diplomatic relations.Footnote ⁴⁶ Without much fanfare, the CJEU simply recognized that international diplomacy is a crucial tool for member states to promote cooperation and friendly relations among themselves, the importance of which goes far beyond EU policy matters and the essence of their international sovereignty equality.

Even though caution is always warranted in any generalizations,Footnote ⁴⁷ there is no denying that the approach to CIL exhibited in Hungary v. Slovakia is precedent-setting with regard to the CIL rules governing the rights and duties accompanying diplomatic relations between EU member states. For example, the right of a receiving member state under CIL to declare the diplomatic and consular agents of a sending member state persona non grataFootnote ⁴⁸ constitutes – following Hungary v. Slovakia – a legally valid limitation of Article 21 TFEU. With a view to the full range of internationally protected and privileged persons,Footnote ⁴⁹ CIL exemptions from Article 21 TFEU go far beyond unwanted visits from foreign head of states. That having been said, CIL distinguishes between the top tier of representatives of a state (head of state, head of government and foreign minister)Footnote ⁵⁰ and other officials as the latter’s status specialis within a foreign country may not extend to private activities, which would then fall under the scope of Article 21 TFEU. As a final note, it should be borne in mind that jurisdictional immunities under CIL are an essential component of diplomatic relations between states, too.

4.4.2 Sovereign Immunity of Member States

Diplomatic and sovereign immunities before foreign courts are primarily relevant as a procedural obstacle to the civil and criminal jurisdiction for domestic courts in EU member statesFootnote ⁵¹ but not for the CJEU. The first and most obvious fact in this regard is that by becoming members of the EU, states waive their sovereign immunities under the EU judicial system. Second, as far as member state officials are bestowed with international immunities under CIL, the EU treaties do not provide for legal action to be taken against any individuals. Consequently, sovereign immunity pleas play no part in proceedings before the CJEU.Footnote ⁵²

However, this does not connote that CIL rules on immunities are immaterial in CJEU proceedings. The right to have access to a court is an inherent element of the fair trial guarantee stipulated in Article 47(2) FRC, which corresponds to Article 6(1) ECHR.Footnote ⁵³ Whenever a member state applies or gives effect to EU law, Article 47(2) FRC and the correspondent fundamental principle of EU law (Article 6(3) TEUFootnote ⁵⁴) protect the individual right of access to a court in that member state.Footnote ⁵⁵ Consequently, EU member states’ obligations under this provision may conflict with CIL immunity rules if, in a domestic court proceeding, the court is precluded from applying EU law due to the defendant’s successful immunity plea.

In 2020, the preliminary ruling in Rina used the above considerations as a point of departure when emphasizing that a national court implementing EU law must satisfy itself that, if it upheld the plea relating to immunity from jurisdiction, the claimants would not be deprived of their right of access to a court.Footnote ⁵⁶ In Rina, the survivors and relatives of victims of the Al Salam Boccaccio 98 ferry disaster in the Red Sea brought an action before the Italian Tribunale di Genova against the Rina group of companies, which are ship classification and certification societies with their seat in Genoa. In the main proceedings, Rina SpA claimed that the Tribunale lacked jurisdiction because the classification and certification operation was carried out under a contract and upon delegation from the Republic of Panama.Footnote ⁵⁷ As a consequence, the Tribunale di Genova asked the CJEU whether or not Regulation 44/2001, commonly known as Brussels I,Footnote ⁵⁸ on international jurisdiction must be interpreted (with due regard for Article 47 FRC) as preventing a member state court from dismissing its jurisdiction due to the defendant’s jurisdictional immunities under CIL.

The CJEU started with the interpretation of the phrase ‘civil and commercial matters’ envisaged in Regulation No. 44/2001 and its delineation to ‘public matters’, which do not fall within the scope of the regulation ratione materiae. After determining that classification and certification operations for ships cannot be considered activities within the scope of decision-making inherent in the exercise of public authority power, the CJEU (after a short reflection on Racke) addressed the impact of Rina SpA’s jurisdictional immunity plea on the application of Regulation No. 44/2001.Footnote ⁵⁹ On the basis of the CIL distinction between acta jure imperii and acta jure gestionis, the latter of which do not trigger customary jurisdictional immunities,Footnote ⁶⁰ the CJEU concluded that:

This rather convoluted phrasing can be read as if a state’s sovereign immunity plea covered by CIL (acta jure imperii) precludes the application of the Brussels I Regulation, an understanding which would be contrary to what Advocate General Szpunar proposed.Footnote ⁶² Indeed, from an international law perspective there is no compelling reason for the EU legislator to preclude the application of Brussels I in cases involving CIL sovereign immunity. As the ICJ pointed out in the Arrest Warrant case, ‘jurisdiction does not imply an absence of immunity, while an absence of immunity does not imply jurisdiction’.Footnote ⁶³ Translated to Rina, Regulation No. 44/2001 (Brussels I) can allocate jurisdiction to a member state’s court without necessarily dealing with CIL immunities as a possible obstacle to the exercise of jurisdiction.Footnote ⁶⁴

In the light of the foregoing, it seems more appropriate to simply read the Rina judgment as an exhortation to domestic courts to interpret Article 1 Regulation No. 44/2001 (Brussels I) on the scope of the regulation’s application (‘civil and commercial matters’) always in line with CIL (acta jure gestionis in contrast to acta jure imperii). This understanding of Rina is backed by Article 1(1) Regulation No. 1215/2012 (Brussels I recast), which is the successor of Regulation No. 44/2001.Footnote ⁶⁵ The provision explicitly clarifies that the regulation does not extend to ‘the liability of the State for acts and omissions in the exercise of State Authority (acta jure imperii)’, with the reference in brackets being a clear nod to CIL immunity rules.Footnote ⁶⁶

Even though Rina is far from being clear on this point, the CJEU’s line of argument strongly indicates that Regulation 1215/2012 (Brussels I recast) is not intended to override the respondent’s sovereign immunity claims under CIL irrespective of whether or not the claim concerns the immunity of a third state or another member state.Footnote ⁶⁷ The fact that the CIL-based sovereign immunities of EU member states are, in principle, valid within the EU’s internal legal sphere can also be deduced from Directive 2009/15/EC on the Common Rules and Standards for Ship Inspection, the sixteenth recital of which states:

In Rina, the CJEU explicitly referred to this recital when pointing out that the EU legislator, in creating EU secondary law, has intended to interpret the rules of CIL on state immunity restrictively.Footnote ⁶⁹ The CJEU’s mentioning of Directive 2009/15/EC, which exclusively concerns member states, is remarkable in two respects: first, the CJEU does not object to the fact that, in principle, member states value their sovereign immunity in another member state’s domestic courts. Second, by emphasizing the directive’s restrictive understanding of state immunity, the Court implicitly recognizes the EU legislator’s role in the constant evolution of CIL by participating in consuetudo and desuetudo through its legislative practice.Footnote ⁷⁰ However, without concurring practice of other states any restrictive understanding of state immunity cannot alter the existing CIL rules created by the international community, a fact the CJEU failed to mention. The question rather is whether Directive 2009/15/EC is evidence of the formation of local CIL on state immunity that deviates from its universal equivalent. The obiter dictum of the CJEU in Rina may indicate this line of reasoning but is methodologically flawed: it ignores that each individual member state, as a sovereign international actor, has legislative intent (opinio juris) distinct from the EU legislator.

4.4.3 Sovereign Equality and the Prohibition of Intervention into Domestic Affairs

Jurisdictional immunities are one of many legal ramifications of the sovereign equality of states, that is, their judicial equality.Footnote ⁷¹ Provided that states exist under the same legal conditions due to their unimpaired sovereignty and exercise of free consent, they all share the capacity to have the same duties and rights under international law. Since 2009, the CIL tenet of sovereign equality has echoed prominently in Article 4(2) TEU (‘The Union shall respect the equality of Member States before the Treaties’), but as a principle it pre-dates the Lisbon Treaty. In 1973, the CJEU argued that:

The CJEU, which tied member states’ equality before community law with the principle of solidarity, did not disclose the exact legal source from which it derived the equality notion. Irrespective of this, the wording chosen by the CJEU in 1973 found its way into the TEU, which did not remedy the revealing absence of the adjective ‘sovereign’ to specify the reason for member states’ equality. This absence is by no means coincidental as, by establishing a supranational Union, EU member states voluntarily and necessarily abandoned many legal manifestations of their sovereignty, the participation of a directly elected European Parliament in the EU law-making process being the most obvious example. That being said, one key expression of sovereign equality that remains firmly in place is captured in essence by Article 4(2) TEU, which elucidates that EU law must equally apply without discrimination to all member states.Footnote ⁷³

In addition, the CIL sovereign equality principle ensures more than states’ equality before the law. Most importantly, the 1970 Friendly Relations Declaration considers the right of each state to freely chose and develop its own political, social, economic and cultural system – a key aspect of states’ sovereign equality.Footnote ⁷⁴ The legal manifestation of this freedom of choice is the prohibition of states to intervene into other states’ domestic affairs, as the ICJ plainly stated in Military and Paramilitary Activities in and against Nicaragua.Footnote ⁷⁵

This principle of non-intervention is firmly rooted in CIL even though certain aspects of the prohibitive rule remain disputed,Footnote ⁷⁶ especially the element of coercion which, according to the ICJ, forms the very essence of the prohibition.Footnote ⁷⁷ States’ domestic affairs protected under CIL are commonly circumscribed as all areas that are not regulated by international law and thus fall exclusively within the state’s domestic jurisdiction (domaine réservé).Footnote ⁷⁸ Building on this notion, it is evident that subject-matter competences of IOs allocated by their constituent instruments are not within the domaine réservé of a member state in relation to the relevant organization and, arguably, in relation to the other member states of that organization; this applies irrespective of the powers an organization enjoys in these policy areas.

Within the EU’s internal legal sphere, there is little room for a non-intervention claim by EU member states, first and foremost because of seventy years of integration that has left few policy areas within the exclusive competence of EU member states (Article 5 TEU and Articles 2–6 TFEU). Recently, the CJEU decided that even though the organizational structure of the domestic judiciary falls within the exclusive competence of member states, the fact remains that, when exercising that competence, the member states are required to comply with their obligations deriving from EU law and, in particular, from Article 19(1) TEU.Footnote ⁷⁹ Because this provision obliges member states to provide remedies that are sufficient to ensure effective legal protection in the fields covered by EU law (Article 47 FRC), the organization of a member state’s domestic judiciary cannot be the domaine réservé exempt from EU interference. As a final observation in this regard, EU primary law lays down certain ideas that form the essential cornerstones of the member states’ political, social and economic systems, all of which must adhere to the fundamental values enshrined in Article 2 TEU.

The above inventory clearly demonstrates that EU law and EU values permeate many aspects of member state politics, even areas that the broader community of states would consider to be matters of exclusive domestic jurisdiction. However, while the CIL principle of non-intervention plays no significant role in the relationship between the EU and its member states, the EU treaties do not ignore member states’ desire for a sacrosanct domestic sphere. As such, Article 4(2) TEU can be considered as a special non-intervention clause that was created to protect member states’ national identities, inherent in their fundamental structures, political and constitutional, inclusive of regional and local self-government from EU overreach.

Admittedly, the clause operates under a different premise than the CIL principle of non-intervention because Article 4(2) TEU protects certain constitutional and political manifestations of national identity within the EU law’s scope of application, that is, beyond member states’ domaine réservé. For example, in several disputes before the CJEU, Article 4(2) TEU has been employed by member states as a justification to restrict the right of free movement (Article 21 TFEU).Footnote ⁸⁰ This notwithstanding, EU primary law, including Article 4(2) TEU, conclusively stipulates the legal conditions under which EU member states’ sovereign freedom to shape the political, social, economic and cultural structures of their polities is constrained and this thus forestalls any recourse to the CIL prohibition of intervention.

This still leaves open the question of what happens if it is not the EU but a member state that intervenes in the domestic affairs of another member state in order to pursue certain policy goals. Thus far the only incident of this kind occurred in 2000 when fourteen member states under the Portuguese EU Presidency imposed diplomatic sanctions on Austria in order to prevent the formation of a new Austrian government coalition with the right-wing Freedom Party accused of xenophobia.Footnote ⁸¹ The suspension of bilateral diplomatic relations beyond the working levelFootnote ⁸² between the fourteen member states and Austria was welcomed by the European Parliament as a measure to protect EU values.Footnote ⁸³ However, the European Commission was far less forthcoming with its support. Indeed, without blaming the fourteen member states for having undermined EU law, the Commissioners unanimously agreed to maintain working relations with the Austrian government unless it breached European treaty provisions on human rights.Footnote ⁸⁴ Given that forming a government is an act of popular sovereignty and the outcome of a democratic process, there is a strong argument that these sanctions intervened into Austria’s domestic affairs.Footnote ⁸⁵ However, the diplomatic sanctions deployed by the fourteen member states lacked the necessary coerciveness to be internationally prohibited under CIL.Footnote ⁸⁶

Thus, imposing diplomatic sanctions and interrupting bilateral communications is a sovereign decision of the sanctioning state that, as a mere unfriendly act, is not regulated by CIL. Assuming member states will in the future deem it necessary to manifest a more forceful reaction to undesirable policy decisions in another member state, for example, by imposing economic, commercial and financial sanctions,Footnote ⁸⁷ any international prohibition on such an intervention under CIL would be fully eclipsed by member states’ obvious violation of the EU treaties, which manifests itself in both member states’ lack of competence in the targeted area and the severe impact on European fundamental freedoms.Footnote ⁸⁸ If, however, the sanctioned member state has indeed infringed EU law or its duties under international law, the question arises as to whether the EU treaties allow other member states to impose countermeasures in accordance with CIL vis-à-vis the law-breaking member state (see Article 49 ASR).

4.4.4 Countermeasures

Back in 1964, the CJEU took the opportunity to clarify its position with regard to the rights of member states to take countermeasures,Footnote ⁸⁹ that is, their right not to fulfil obligations under the EU treaties in reaction to a wrongful act committed by EU institutions.Footnote ⁹⁰ In substance, the dispute concerned taxes introduced by Luxembourg and Belgium in 1958 that resulted in an effective increase in the intra-community customs barriers. Luxembourg and Belgium claimed that they should be considered released from the EU treaty obligations because the EU institutions had themselves failed to meet their obligations. In rejecting this argument, the CJEU declared:

Analysing the judgment, then CJEU judge Lecourt revealed that the CJEU wanted to make a strong point that no unilateral legal acts of member states could prevail against the EU treaties because the member states had renounced the ability to take self-help action to enforce their legal rights.Footnote ⁹² By excluding this decentralized means of law enforcement within the EU treaties’ scope of application, the CJEU construed the EU as a self-contained regime with the EU treaties providing end-to-end secondary rules, not only with regard to the legal consequences of any breach of EU law but also with regard to the means of dispute settlement and law enforcement.

Of course, in that case the CJEU did not have any doubts that all EU law enforcement mechanisms were fulfilling their assigned functions. However, this is not something that should be taken for granted. Prominent authors such as Simma argue that the general regime of state responsibility can be called on as a means of last resort after all remedies provided by the subsystem have been exhausted without positive results and further tolerance of the imbalance of costs and benefits caused by any non-performance can no longer bona fide be expected from the injured party.Footnote ⁹³ Obviously, in the highly integrated EU legal order it is difficult to establish when the costs–benefits balance is thus so jarringly thrown out of balance. For example, Poland’s recent reorganization of its domestic judiciaryFootnote ⁹⁴ has been cited by the European Commission as a serious rule of law violation (Article 2 TEU), which led to successful infringement procedures before the CJEUFootnote ⁹⁵ and preliminary rulings from procedures initiated by domestic courts.Footnote ⁹⁶

However, judicial proceedings can only provide relief in specific cases and are unable to address any systemic flaws in member states’ conduct.Footnote ⁹⁷ To overcome this, the Commission triggered its general rule of law framework, which is designed to supplement legal proceedings under Article 258 TFEU as well as the political mechanism under Article 7 TEU, a means of recourse colloquially referred to as the ‘nuclear option’ of the EU rule of law defence system. Due to a lack of progress in the situation with Poland, in 2018 the Commission activated, for the first time in EU history, Article 7(1) TEU. Unfortunately, the Council’s subsequent indecision made the ‘nuclear option’ ineffective, which gives rise to the question of whether a systemic Article 7 failure can open the gate to allow bilateral CIL countermeasures to be taken by concerned EU member states.

There are a number of serious legal arguments against the right of individual member states under EU law to take ultima ratio recourse to CIL countermeasures if another member state is in serious breach of EU values. First and most importantly, such recourse to CIL countermeasures would affect the allocation of responsibilities defined in the EU treaties, which in other contexts the CJEU has repeatedly rejected for the sake of protecting the EU legal order’s autonomy.Footnote ⁹⁸ Such interference with EU powers and competences also impacts the international lawfulness of member states’ countermeasures: they are unlawful under CIL if they affect the rights of third parties, including the EU. Second, Article 344 TFEU obliges member states to not submit their disputes over the interpretation and application of the EU treaties to any methods of settlement other than those provided in the EU treaties.Footnote ⁹⁹ The provision can certainly be understood as protecting not only the CJEU’s monopoly on judicial dispute settlement but also Article 7 TEU and its coercive sanctions system.Footnote ¹⁰⁰ Consequently, there is no room for such recourse to CIL countermeasures within the EU’s internal legal sphere.

4.4.5 Law of Treaties

5.2.1 The Flexible Methodology Used by the International Court of Justice to Identify Customary International Law

Article 38 of the Statute of the International Court of JusticeFootnote ⁵ conceives international custom as ‘general practice’ (material element) that has been ‘accepted as law’ (subjective element) by states.Footnote ⁶

5.2.2 The Role of Consensus in the Process of Identification of Customary International Law

We argue that the notion of consensus is a useful tool to address the challenges identified above. This notion can be conceived from both a formal and a substantive dimension. From a formal perspective, consensus constitutes a decision-making mechanism. Within the UN system, it has been defined by the Office of Legal Affairs as the ‘adoption of a decision without formal objections and vote; this being possible only when no delegation formally objects to a consensus being recorded, though some delegations may have reservations to the substantive matter at issue or to a part of it’.Footnote ³³ From a substantive perspective, consensus implies a general agreement among the subjects of international law.Footnote ³⁴ In the latter context, the notion of consensus represents their common interests and allows states to identify the content of the international rules applicable in their relations.

In the framework of CIL, it can be said that its formation, amendment and termination stems from the agreement reached jointly by the states (consensus generalis). This consensus generalis does not imply unanimity and may appear not only through constant and uniform repetition of a practice (material element), but also through the efforts undertaken at an institutional level, such as the conclusion of multilateral treaties and/or the resolutions adopted by the General Assembly (subjective element).

From a theoretical point of view, a consensus-based approach to CIL escapes the demands imposed by the most extreme voluntarist doctrines,Footnote ³⁵ inasmuch as it does not require explicit evidence of the consent of all states to the acceptance of customary rules of a general scope.Footnote ³⁶ Further, this approach safeguards the autonomy between the material and the subjective elements of CIL,Footnote ³⁷ therefore allowing the judicial organ to flexibly apply the two-element approach in accordance with the circumstances of each dispute.

The ICJ (as well as other international courts and tribunals) can identify customary rules that have reached general acceptance (consensus generalis) by applying the two-element approach in a flexible manner. In this vein, the notion of consensus adds flexibility to the methodology used by international courts and tribunals to identify CIL. At the same time, consensus prevents any unsupported practices from assuming the category of CIL.Footnote ³⁸

However, this ‘consensualist approach’Footnote ³⁹ is not exempt from technical challenges. Consensus-based decisions adopted within the framework of international institutions do not in fact guarantee the identification of a customary rule. It is necessary to make further analysis of state practice. The formal dimension of consensus, that is, the adoption of consensus-based decisions by the General Assembly, may be indicative of the subjective element (opinio juris), but often contains veiled objections that can only be identified through a comprehensive analysis of state practice.Footnote ⁴⁰ Though a complete examination of the ICJ’s case law exceeds the scope of this study, some traces of the ‘consensualist approach’ can be found with relation to contentiousFootnote ⁴¹ and advisoryFootnote ⁴² cases. In essence, this approach allows the use of both induction and deduction in the identification of CIL. The use of one or the other depends on the particular circumstances of each case, as well as the legal framework and the conduct of the parties to the dispute. Further, in accordance with the two-element approach, a more detailed study of state practice is required in the case of customary rules with a more limited scope of application or for those that are contested by the disputing parties.

In using the notion of consensus, the ICJ emphasizes the value of the codification works undertaken by the ILC. In a time marked by the absence of codification conventions, the ILC should therefore not give up the task (not less important) of adopting instruments that allow the identification of customary rules generally accepted in state practice.

5.3.1 Explicit Interaction

The resolutions adopted by the General Assembly by consensus can declare, crystallize or even generate new customary rules. This occurs when the consensus reached during their adoption (formal dimension) implies a consensus generalis (substantive dimension). This consensus generalis must be representative of the general agreement of states and confirmed by state practice.

Since the ICJ has recognized this legal interaction, it is labelled in this chapter as ‘explicit interaction’. In Military and Paramilitary Activities in and against Nicaragua, the ICJ identified a customary rule regarding the non-intervention in internal affairs from Resolution 2625 (XXV).Footnote ⁵⁰ The ICJ took into account its generalized acceptance by states and, employing a deductive method, concluded its mandatory nature.Footnote ⁵¹ The ICJ further applied the inductive method and examined the subsequent practice of states to discard the possibility of exceptions to this rule of non-intervention.Footnote ⁵² In Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 the ICJ recalled that Resolution 1514 (XV) of the UN General Assembly,Footnote ⁵³ granting independence to colonial countries and peoples, ‘has a declaratory character with regard to the right to self-determination as a customary norm, in view of its content and the conditions of its adoption’.Footnote ⁵⁴ Based on an inductive analysis of the subsequent practice of states, the ICJ considered that Resolution 1514 (XV) had created a customary rule binding on all subjects of international law.Footnote ⁵⁵

The CJEU has approached the explicit legal interaction (between the resolutions adopted by the General Assembly and CIL) with caution. References to resolutions adopted by the General Assembly have been frequent in its most recent practice. However, as is analysed below, the CJEU has sometimes preferred to evaluate their interplay with EU law, by resorting to legal principles. In the next section, we comment two cases where resolutions adopted by the General Assembly were invoked by the CJEU both from a material perspective and from a formal perspective.

5.3.2 Implicit Interaction

In other cases, the CJEU articulates the identification of CIL resorting to legal principles. Despite the fact that there are references to general principles of international law in some precedents of the ICJ, this judicial organ has neither lavished on them, nor it has recognized the existence of a legal interaction between CIL and general principles of international law. This issue has been addressed differently by the CJEU. On some occasions, this technique of implicit interaction has produced ‘particularist’ results before the CJEU, as the case is finally settled in accordance with a legal principle recognized within EU law. At other times, when the CJEU uses a general principle of international law, the judgment could be classified as ‘generalist’.

6.2.1 Peremptory Norms as Hierarchy: The Kadi Saga

Kadi was important for many reasons, an important one being the articulation, in unusually intricate circumstances, of the basic tenets of the relationship between EU law and international law. On this matter, the respective decisions of the General Court and the CJEU evidence that at least two different understandings of the relations between those legal orders are possible. As I shall explain, each one is based on a different understanding of the autonomy of EU law as a reflection of the self-contained character of this legal order. In the case at hand, the ‘triggering factor’ (the element that raised the question of the limits of EU law’s autonomy) was the rule of primacy enshrined in Article 103 UN Charter,Footnote ⁴ which reads as follows:

The facts of the case are well known: Mr Kadi, a Saudi businessman, challenged the legality of an EU regulation imposing on him certain restrictive measures due to his alleged association with Usama bin Laden, the Al-Qaeda network and the Taliban.Footnote ⁵ The regulation followed the adoption by the UN Security Council of binding measures under Chapter VII of the UN Charter.Footnote ⁶ At stake was an alleged violation of fundamental rights resulting from the implementation of such measures by the United Kingdom.

The General Court reasoned as a ‘pure’ international court. It considered that reviewing the relevant EU legislation implementing Security Council resolutions would have entailed an ‘indirect review’ of such resolutions in the light of EU law standards.Footnote ⁷ According to the Court of First Instance (CFI), both international and EU law precluded this possibility. To this effect, the CFI invoked Article 103 UN Charter and Article 27 Vienna Convention on the Law of TreatiesFootnote ⁸ (VCLT), as well as the obligation binding on EU institutions to exercise their powers in accordance with international law.Footnote ⁹ These elements were pivotal to the analysis and, following the General Court’s logic, would have sufficed to conclude that the EU is bound to implement the Security Council resolutions. However, the General Court did not stop there. Without explaining the jurisdictional basis for its finding, it ruled that it was competent to review the lawfulness of Security Council resolutions in the light of jus cogens norms,

After carefully scrutinizing the measures decreed by the Security Council against several international human rights norms having jus cogens status (including, somewhat puzzlingly, the right to property and the right to be heard by a sanctioning authority), the General Court concluded that no breach had been caused to the applicant’s rights.

On appeal, the CJEU reasoned as a domestic court. It saw no challenge to the authority of the Security Council in reviewing EU legislation adopted in implementation of Security Council resolutions against EU human rights standards. The CJEU made no single reference to peremptory norms. Instead, the reasoning was emphatically grounded on the autonomy of EU law, which assumes the separate nature of the hierarchy of sources of this order and, by extension, subordinates the reception of international law to EU primary law.Footnote ¹¹ In other words, the CJEU considered that the autonomy of EU law operates vis-à-vis international law regardless of the primacy of the UN Charter. On this basis, the CJEU focussed the analysis on the internal legality of EU legislation implementing the relevant Security Council resolutions and concluded that the EU had breached certain fundamental rights of the applicants as protected by EU law.

It is to be noted that both the General Court’s and the CJEU’s approaches were framed in terms of hierarchy,Footnote ¹² yet on this point an important nuance existed between the two. The General Court’s rigid, formalistic understanding of the relations between legal orders showed strong deference to the Security Council, except for the (somewhat surprising) analysis of the legality of the relevant Security Council resolutions in the light of jus cogens. For its part, the CJEU’s approach (which differed from Advocate General (AG) Poiares Maduro’s proposals in many respectsFootnote ¹³) can be characterized as both dualistic and pluralistic.Footnote ¹⁴ It was dualistic because it identified ‘domestic law’ (here, EU law) as the ultimate foundation for the determination of the conditions of reception of international law, on the basis the principle of autonomy. But it was also pluralistic in that the CJEU built ‘systemic bridges’ with international law by referring to the doctrines of consistent interpretation of EU law in the light of international law and ‘equivalence’. According to the latter doctrine (imported from the case law of the European Court of Human Rights (ECtHR)), the CJEU does not review the legality of decisions made by another international organization as long as said organization offers an ‘equivalent’ level of protection of fundamental rights.Footnote ¹⁵

On balance, this is a story of avoidance of peremptory norms by the supreme interpreter of EU law. This outcome was understandable if we consider that the normative conflict at stake did not originate in EU law (i.e. there was no rule of EU law contradicting a peremptory norm of international law), but rather had its source in an obligation of international law enshrined in a Security Council resolution. This enabled the CJEU to avoid the broader legal implications of Mr Kadi’s legal situation.Footnote ¹⁶

Accordingly, not much can be gained from the Kadi saga in terms of understanding the nature and legal effects of peremptory norms in general international law. The lesson to be learnt, if any, is that such norms do not blur the line separating international from domestic law by overturning the conditions for the interaction between legal orders.Footnote ¹⁷ This does not mean, though, that the General Court’s findings have been left behind in the drawer of judicial expeditions. Indeed, the General Court’s formalistic understanding of the hierarchy of peremptory norms is echoed by Article 3 ILC’s draft conclusions on peremptory norms, which provides that peremptory norms ‘are hierarchically superior to other rules of international law’. I shall return to this question below.

6.2.2 Peremptory Norms as Interpretation: The Western Sahara and Front Polisario Cases

The Western Sahara and Front Polisario cases evidence similar patterns of avoidance of peremptory norms. The cases concerned the legality of certain decisions made by the Council to authorize the conclusion of certain agreements between the EU and Morocco: on the one hand, an Agreement between the European Union and the Kingdom of Morocco concerning Reciprocal Liberalisation Measures on Agricultural Products, Processed Agricultural Products, Fish and Fishery ProductsFootnote ¹⁸ (‘the Liberalisation Agreement’, discussed in Front Polisario); on the other, a Fisheries Partnership Agreement between the European Community and the Kingdom of MoroccoFootnote ¹⁹ (‘the Fisheries Agreement’, discussed in Western Sahara) and a Protocol between the European Union and the Kingdom of Morocco setting out the fishing opportunities and financial contribution provided for in the Fisheries Partnership Agreement between the European Union and the Kingdom of MoroccoFootnote ²⁰ (‘the Fisheries Protocol’, also discussed in Western Sahara). Both cases turned around the applicability of those treaties in the territory of Western Sahara in the light of the principles of self-determination and a people’s sovereignty over its own natural resources.Footnote ²¹ A particularly controversial matter (the elephant in the room) was the question of the status of Morocco vis-à-vis Western Sahara.Footnote ²² The judgments cover many issues that cannot be addressed here. What follows is a brief outline of some key points prior to an analysis thereof.

6.3.1 The Nature of Peremptory Norms in the Debates of the International Law Commission

On 31 May 2019, the ILC adopted on first reading a text containing twenty-three draft conclusions and a draft annex on peremptory norms.Footnote ⁵⁴ In preparation of this work, Special Rapporteur Tladi produced four reports which define peremptory norms first and foremost in terms of non-derogability.Footnote ⁵⁵ This is a point on which there is broad doctrinal agreement, for only the ‘negationists’ of jus cogens would reject the existence of norms producing such effects.Footnote ⁵⁶ It therefore comes as no surprise that Draft Conclusion 2 (which follows in this respect Article 53 VCLT) received broad support from both ILC members and UN member states. According to this provision:

Also on the basis of Article 53 VCLT, Mr Tladi identified another ‘essential’ characteristic of jus cogens: it is based on a norm of general international law.Footnote ⁵⁸ This question was considered in his Second Report, dealing inter alia with the sources of peremptory norms.Footnote ⁵⁹

Going beyond the text of the VCLT, the Special Rapporteur referred to the existence of other ‘core characteristics’ of jus cogens, which in his view are supported by doctrine and the practice, inter alia, of international courts. These are the protection of fundamental values of the international community, hierarchical superiority to other rules of international law and universal application. Following some internal discussion regarding the place of these elements in the project, the ILC decided to insert them into Draft Conclusion 3 under the ambiguous title ‘General nature of peremptory norms of general international law (jus cogens)’. In so doing, the Drafting Committee assumed the proposal, made by various members of the Commission, to exclude the abovementioned characteristics from the scope of the ‘definition’ of peremptory norms advanced in Draft Conclusion 2. In other words, as Draft Conclusion 3 stands now, the attributes of protection of fundamental values, hierarchical superiority and universality are more ‘declaratory’ than ‘constitutive’ elements of peremptory norms.Footnote ⁶⁰ Hereinafter, I shall outline such attributes with an emphasis on the ‘universal’ nature of peremptory norms.

The proposition that peremptory norms protect the fundamental values of the international community is based on the premise that they constitute a selected body of norms reflecting the moral foundations of the international legal order (ordre public).Footnote ⁶¹ Mr Tladi’s reports cite abundant authorities in support of this conclusion, including case law of international courts and tribunals.Footnote ⁶² This is not the place to take stock of this debate (the Special Rapporteur’s reports are extensive in this regard). It will be noted, however, that this view is not unanimously shared by those who have theorized on peremptory norms, as Mr Tladi’s himself notes. In particular, well known is the opinion of Robert Kolb, who contends that jus cogens is a technique of protection of the integrity of any legal regime that applies not only to public order, but also to certain necessary rules of international law such as good faith and pacta sunt servanda (‘logical jus cogens’) and to particular legal regimes that cannot operate without certain rules and principles (‘public utility jus cogens’).Footnote ⁶³

The question of the link between jus cogens and the fundamental values of international law relates to another attribute of these norms: hierarchical superiority. According to the Special Rapporteur, ‘[t]he idea of rules capable of invalidating others and permitting no derogation implies a normative hierarchy’; it is ‘both a result and reflection of normative superiority’.Footnote ⁶⁴ This proposal was in general well-received by ILC members,Footnote ⁶⁵ even if they seemed to disagree on the consequences of such hierarchy: while one member indicated that it is ‘not clear how describing jus cogens norms as “hierarchically” superior to other norms of international law enhanced their peremptory nature or non-derogability’,Footnote ⁶⁶ another contended that:

This brings us to the third ‘core’ characteristic of jus cogens: universality. Citing abundant doctrine and jurisprudence, Mr Tladi’s first report on peremptory norms explained that ‘the characteristic of universal applicability flows from the notion of non-derogability, that is, it is difficult to see how a rule from which no derogation is permitted can apply to only some States’.Footnote ⁶⁸ Accordingly, he inferred that the basis for the existence of peremptory norms of a regional nature ‘remains obscure’.Footnote ⁶⁹

The latter conclusion received mixed reactions from ILC members. While some agreed that universal reach is part of the very essence of jus cogens,Footnote ⁷⁰ others criticized the Special Rapporteur for having taken such a conclusive stand at an early stage of the ILC’s work on the topic.Footnote ⁷¹ Perhaps in reaction to these comments, the matter was discussed in great detail in the Special Rapporteur’s fourth (and last) report. Therein Mr Tladi, while noting that some scholars have supported the existence of jus cogens norms of regional reach, pointed to the existence of various problems arising from this concept: the absence of state practice,Footnote ⁷² the consequences of the opposition by a would-be ‘regional state’ to a regional peremptory norm,Footnote ⁷³ the definition of ‘region’,Footnote ⁷⁴ the connection between regional jus cogens and treaty regimes having a regional character,Footnote ⁷⁵ the exceptional nature of jus cogens norms,Footnote ⁷⁶ and most importantly, the unclear legal consequences of a breach of these norms.Footnote ⁷⁷ His analysis of these questions recalled the fundamental objection that there is neither international practice nor broad doctrinal support for this notion.Footnote ⁷⁸ Accordingly, Mr Tladi recommended not to include any draft conclusion on the matter and limit the discussion to the ILC’s commentary.Footnote ⁷⁹

A majority of ILC members supported this view,Footnote ⁸⁰ although others expressed disagreement or hesitations. Some cited two decisions made by EuropeanFootnote ⁸¹ and Inter-American human rights mechanisms.Footnote ⁸² Overall, most ILC members agreed that, regardless of the existence of regional peremptory norms, it was not necessary to settle a discussion that, in their view, was outside the ILC’s mandate. Among the ‘dissenters’, one member explained that the term ‘general international law’ ‘simply indicated that, at the time of adoption of the VCLT, regional jus cogens was considered to be outside the scope of article 53 [of the Vienna Convention]’.Footnote ⁸³ Another member explained that jus cogens does not only exist in the ‘narrow framework provided by the Vienna Convention’ and added that:

Leaving these discrepancies aside, a clear majority of ILC members viewed regional peremptory norms as a threat to the universal nature (and effectiveness) of peremptory norms. This was also the line followed by those UN member states which made comments on the matter before the Sixth Committee of the General Assembly.Footnote ⁸⁵

6.3.2 The European Union’s Contribution to the Debate: Case Law on Foundations

In assessing the features that distinguish EU law from international and domestic law, the CJEU has identified various basic parameters that underpin the autonomous nature of this body of norms. Some of them bear a striking resemblance to the peremptory norms of general international law. This must not come as a surprise: as an integrated legal order regulating the exercise of public authority, it seems natural that EU law bears some ‘core features’ that cannot be altered without affecting its ‘very essence’.

An important difference with international law relates to the doctrinal context in which such basic parameters were set out. In international law, peremptory norms emerged as a limit to unfettered state consent, which post-war scholarship (and many states) viewed as a threat to the protection of basic human values and state interests.

In EU law, the identification of ‘basic parameters’ by the CJEU fulfils an assertive dual function: the protection of both the autonomy and effectiveness of EU law vis-à-vis both domestic and international law.Footnote ⁸⁶ The ‘very essence’ of EU law has been discussed mostly in the context of external relations law, notably in CJEU decisions dealing with treaties that contain third-party dispute settlement mechanisms. Therein the CJEU has referred to the existence of ‘foundational principles’ from which no derogation is permitted. However, the clearest formulation of the hierarchical consequences of those principles was made in Kadi, where the CJEU recalled that EU member states are not allowed to ‘derogat[e] from the principles of liberty, democracy and respect for fundamental rights and fundamental freedoms enshrined in Article 6[1] as a foundation of the Union’.Footnote ⁸⁷ In relation to a treaty clause enabling member states to derogate from EU law in order to comply with treaties concluded prior to the Treaty of Rome, the CJEU even affirmed that:

At least two commentators have contended that, in placing certain values above the rules of primary law enshrined in the treaties, this passage advanced a new development: the recognition of a form of supra-hierarchy in EU law which contradicted the General Court’s reliance on the superior nature of the peremptory norms of general international law in EU law.Footnote ⁸⁹ However, without prejudice to our analysis below, Kadi did not advance a radical innovation in this regard. Rather, it must be read together with other decisions where the CJEU sketched a similar normative phenomenon.Footnote ⁹⁰ For example, in Opinion 1/76, the CJEU referred to the ‘internal constitution of the Community’, the ‘essential elements of the Community structure’ and ‘the very concepts of the Community and its common policy’ in assessing an international agreement that established a fund which altered the powers of the Community and the relations between its member states in the field of common commercial policy.Footnote ⁹¹

In Opinion 1/91, the CJEU referred to ‘the very foundations of the Community’ in relation to the protection of its own powers. The decision concerned the legality of the agreement establishing the European Economy Area (EEA). Said agreement enabled an international court (the envisaged EEA Court) to deviate from future interpretations by the CJEU of the rules of (then) European Community (EC) law when interpreting the equivalent provisions of the EEA agreement.Footnote ⁹² In the same decision, the CJEU referred to the principles of primacy and direct effect as one of ‘the essential characteristics of the community legal order’.Footnote ⁹³

In Opinion 1/00, the CJEU reiterated the ‘essential character’ of certain powers of that court (which it linked to the autonomy of EU law).Footnote ⁹⁴ Therein, the CJEU differentiated between, on the one hand, impingements on ‘the powers of the Community and its institutions, or the canons of interpretation of Community law’ by means of the conclusion of an international treaty, and on the other, impingements ‘to such an extent as to alter their essential character’.Footnote ⁹⁵

In Opinion 1/09, the CJEU characterized the reference for a preliminary ruling mechanism as ‘essential for the preservation of the Community character of the law established by the Treaties’.Footnote ⁹⁶

In Opinion 2/13, the CJEU first considered that the EU’s ‘very nature’ precludes this organization from being considered a state when it concludes international agreements.Footnote ⁹⁷ Next, the CJEU differentiated between, on the one hand, the ‘specific characteristics of the EU and EU law’ (including ‘those relating to the constitutional structure of the EU’),Footnote ⁹⁸ and on the other, the ‘specific characteristics arising from the very nature of EU law’ (the independent source of EU law, primacy and direct effect).Footnote ⁹⁹ The values enshrined in Article 2 TEU were described as ‘the fundamental premiss’ of the EU’s legal structure,Footnote ¹⁰⁰ while the fundamental rights protected by the EU Fundamental Rights Charter were situated ‘at the heart of that legal structure’.Footnote ¹⁰¹

The CJEU revisited this case law when rendering a judgment on Brexit:

In Opinion 1/17, the CJEU referred again to the ‘essential character’ of the powers of EU institutions, the ‘essential characteristics of the European Union and its law’ and ‘the founding values set out in Article 2 TEU’ in its analysis of the investor-state dispute settlement mechanism provided for in the Comprehensive Economic and Trade Agreement concluded between the EU and Canada.Footnote ¹⁰³

Moreover, in two landmark cases concerning state derogations from the EU principles of free movement of goods and services, the CJEU considered fundamental rights to be a valid justification for such derogations. While it is true that the EC Treaty already contained a ‘domestic public policy’ derogation clause that justified such a restriction, the CJEU grounded its reasoning not so much in the ‘internal’ reasons of the state, but rather in the protection of fundamental rights under EU law:

6.3.3 Traces of Peremptoriness in European Union Law?

The above account shows that the list of potential peremptory norms in EU law is extensive and varied.Footnote ¹⁰⁵ It encompasses values and principles linked to the protection of a European public order (liberty, democracy and fundamental rights), rules concerning the basic constitutional structure of the EU (such as the exclusive jurisdiction of the CJEU to interpret EU law) and principles concerning the political relations between the EU and its member states (solidarity), as well as principles concerning the legal relations between the EU and its member states (autonomy, primacy and direct effect). For the sake of convenience, I shall refer to these rules, principles and values as ‘the foundational elements of EU law’. Among these, my analysis shall focus on the first category, namely the values and principles enshrined in Article 2 that are most closely related to the protection of a European public order.

The extensive nature of this list may call the peremptory nature of such foundations into question, in line with Mr Tladi’s argument that peremptory norms are ‘exceptional’. However, there is no reason why a regional system may not develop a broader typology of peremptory norms in accordance with its specific needs; indeed, the concept of peremptoriness is inherent to the existence of a legal order. In the words of Virally,

The EU’s constitutional and legal structure is embedded in principles of both domestic constitutional and international law;Footnote ¹⁰⁷ it is therefore logical that its highest rules mirror the specific characteristics of this dual structure. In constitutional law, as is well known, several constitutional courts have identified certain core principles (national identity, fundamental rights, internal distribution of powers, etc.) in discussing the limits to the increasing allocation of state power to the EU. Such principles have been defined as so fundamental to the preservation of the constitutional order that they cannot be delegated or transferred to the EU.Footnote ¹⁰⁸

To this argument, it must be added that the precise scope of peremptory norms in general international law is debated. While the mainstream position (as reflected in Article 3 ILC’s draft conclusions) views jus cogens as located at the top of the hierarchy of norms limiting state consent on the basis of fundamental values, the argument has also been advanced that jus cogens includes, but also goes beyond, the protection of public order. These additional forms of peremptoriness (defined by Robert Kolb as ‘public utility’ and ‘logical’ jus cogens) would reflect purely normative needs of international law as a legal system.Footnote ¹⁰⁹

It is therefore no surprise that the imperative norms of EU law are broader in nature and function. Indeed, the more sophisticated structure of the EU’s foundational elements is the result (at least in part) of institutional differences in the allocation of the ultimate power to settle normative conflicts involving ‘core’ norms and principles. As is known, such allocation is inorganic in conflicts concerning general international law. The judicial organ best suited, at least in theory, to structure and give content to the highest principles of public international law (the ICJ) has been so far reluctant to play that role.Footnote ¹¹⁰ Conversely, in EU law the CJEU has embraced this task with enthusiasm, as shown by the decisions outlined in Section 6.3.2.Footnote ¹¹¹

Turning now to the question of legal effects, the main consequence of a breach of the foundations of EU law is the invalidity of norms in conflict with the ‘higher’ norm. From this point of view, there is no substantial difference with general international law. Nor is there any substantial difference with respect to, inter alia, other rules of EU primary law: in the end, invalidity is an ordinary consequence in any structured legal order. Therefore, in order to understand the ‘special nature’, under EU law, of the invalidating effects of its foundational elements, one must look for specific indicators (or ‘declaratory elements’, to borrow the term used by the ILC) that reflect the existence of a special hierarchy of norms.

The CJEU’s opinions regarding the conclusion of international treaties may be an adequate candidate in that they tested the unique characteristics of certain principles, norms and values at the core of EU law. However, their relevance is limited in that in none of these cases did the CJEU draw ‘extraordinary’ consequences (in EU law terms) from the eventual conflict between the international treaties at stake and the EU’s foundational elements – it could not be otherwise, given the limited nature of the CJEU’s jurisdiction under Article 218.11 TFEU. The same applies to those judgments (such as Achmea) where the Court identified a conflict between a foundational element of EU law and an international treaty concluded between member states.

Accordingly, one must look elsewhere for ‘special effects’. A possible candidate is the conflict clause enshrined in Article 351 TFEU.Footnote ¹¹² Such a clause is a rare example of a rule within the system enabling member states to override their primary law obligations in order to comply with a rule outside the system which, by virtue of Article 351 TFEU, is placed (at least temporarily) at a horizontal level with the treaties. Admittedly, this is not a case of derogation strictu sensu, as shown by the obligation enshrined in Article 351.2 TFEU to ‘take all appropriate steps to eliminate the incompatibilities established’ between EU law and an international treaty concluded before 1 January 1958. However, in Kadi the incompatibility between the obligations arising from the UN Charter and the protection of certain fundamental rights resulted in the invalidation of an internal act that otherwise may have been authorized by the primary rule enshrined in Article 351 TFEU. It is for this reason that, as indicated above, this passage of Kadi has been interpreted as reflecting a ‘supra-hierarchy’ in EU law.Footnote ¹¹³

It may be argued that, even in that case, the legal consequences of the normative conflict were limited to the annulment of an internal act in breach of fundamental rights. In my view, this passage of Kadi was an expression of the basic premise that peremptory norms operate within the limits of a legal system. They do not ‘cross’ systemic boundaries. In Kadi, the invalidating legal effects of the protection of fundamental rights in EU law remained internal to the system and, indeed, could only remain internal to the system without affecting the validity of incompatible treaties or (in that case) Security Council resolutions. By the same token, not even the most sacred rule or principle of EU law can invalidate acts of domestic law. The same logic applies to the peremptory norms of general international law, which cannot invalidate incompatible domestic law provisions.

Aside from norm invalidation, state responsibility is another important feature of the foundations of EU law, and more particularly of the values reflected in Article 2 TEU (namely, liberty, democracy and the protection of fundamental rights). According to Article 7(3) TEU, a member state may be sanctioned with a loss of voting rights in the Council if the European Council determines the existence of ‘a serious and persistent breach by a Member State of the values referred to in Article 2 [namely, liberty, democracy and the protection of fundamental rights]’. This mechanism is preceded (inter alia) by a Council determination of the existence of a ‘clear risk of a serious breach by a Member State’ of the abovementioned values (Article 7(1) TEU).Footnote ¹¹⁴

Here, the parallelism with the mechanism of enhanced responsibility of general international law (assuming that Article 41 of the Articles on Responsibility of States for Internationally Wrongful Acts (ARS) is a reflection of general international law) is more obvious, as both European and international peremptory norms are linked to the protection of fundamental values understood as public order. Indeed, with respect to general international law, such values were defined in the Commentary to Article 40 ARS as ‘those substantive rules of conduct that prohibit what has come to be seen as intolerable because of the threat it presents to the survival of States and their peoples and the most basic human values’.Footnote ¹¹⁵

A final point to consider concerns what may be labelled as the ‘Brexit’ argument, which may be explained as follows: while, in general international law, peremptory norms do not enable ‘individual’ opting-out, in EU law member states are free to withdraw from the system (including its highest norms and principles) in accordance with Article 50 TEU. This defeats the peremptory nature of such norms and principles, and by extension the possibility of a regional jus cogens. This is another variation of the claim that jus cogens is by necessity universal. Suffice it to recall that jus cogens reflects the characteristics of the legal order where it operates. In EU law, the reference point is not so much general international law but rather domestic law: as much as a sub-federal unit may ‘escape’ the jus cogens of the federation by becoming independent and adopting its own peremptory norms, so could a member state ‘escape’ the jus cogens rules of the EU by exiting the organization. In neither of the two instances would peremptory norms lose their special value.