The Court of Justice of the European Union (CJEU)1 is often criticized for judicialization of politics and at times, the CJEU is called into the terrain of megapolitics. The posting of workers in the European Union (EU) is such a terrain of mega-politics, characterized by deep conflicts between EU free movement principles and national social protection. A “posted worker” is employed in one EU member state, but temporarily sent by his or her employer to another EU member state to provide a service. Since posted workers do not migrate permanently, they principally remain subject to the law of their sending country. They are also entitled to a core of rights in the receiving country. This constellation triggers fundamental questions about social justice between and within EU member states, which are mega-political in all three respects theorized in the introduction to this special issue.2 At the inter-state level, the basic question is which country’s labour and social regulation applies to posted workers. At the societal level, the opportunity for firms to rely on workers governed by foreign rules may call into question domestic compromises between capital and labour, like wage levels and social security. Finally, conflicts about the posting of workers invoke sovereignty concerns, begging the question of how to balance the freedom to provide services, protected by EU rules, and the regulation of labour relations, regarded as a matter of national sovereignty by EU member states.