Recently, the World Trade Organization (WTO) granted Mexico the right to retaliate against the US as a compensation for losses related to the US ‘dolphin-safe’ label (May 2017). Despite the diversity of works on the issue, few analyze the changes in the US approach to dolphin protection as a result of international and domestic pressures related to the tuna–dolphin controversy. This paper seeks to understand such changes and their consequences using the process tracing method. It shows that (1) the US approach to dolphin protection passed through a process of policy change motivated by trade and diplomatic concerns mediating dolphin protection, and that (2) it was partially reversed in court as an outcome of the concessions offered to get the policy change approved. Finally, the paper argues that (3) this process led to the lock-in of the US ‘dolphin-safe’ label and to its expansion in response to recent WTO decisions.