One counterintuitive variation in wage-setting regulation is that countries with the highest labor standards and strongest labor movements are among the least likely to set a statutory minimum wage. This, the author argues, is due largely to trade union opposition. Trade unions oppose the minimum wage when they face minimal low-wage competition, which is affected by the political institutions regulating industrial action, collective agreements, and employment, as well as by the skill and wage levels of their members. When political institutions effectively regulate low-wage competition, unions oppose the minimum wage. When political institutions are less favorable toward unions, there may be a cleavage between high- and low-wage unions in their minimum wage preferences. The argument is illustrated with case studies of the UK, Germany, and Sweden. The author demonstrates how the regulation of low-wage competition affects unions’ minimum wage preferences by exploiting the following labor market institutional shocks: the Conservatives’ labor law reforms in the UK, the Hartz labor market reforms in Germany, and the European Court of Justice's Laval ruling in Sweden. The importance of union preferences for minimum wage adoption is also shown by how trade union confederation preferences influenced the position of the Labour Party in the UK and the Social Democratic Party in Germany.