Despite the presence of hyper-mobile migrant workers in the European Union, there is very little research on transnational union organizing efforts. This paper examines the European Migrant Workers Union (EMWU), which signalled a shift by the German union Industriegewerkschaft Bauen-Agrar-Umwelt (IG BAU) in its approach to migrant workers away from national protectionism and toward transnational organizing. The EMWU, however, failed to thrive as an organization, primarily because of decisions by other unions to reject the transnational approach and instead to defend existing jurisdictions. We argue that this inaction constitutes a setback for union reassertion of control over markets and for bringing industrial citizenship to Europe’s hyper-mobile workers.