National systems have provided unions with stronger institutional power resources by comparison to the EU structures governing the Single Market. In aviation, EU governance rules empowered Ryanair to defeat all European pilot unions, regardless of the different national varieties of structural, associational, or institutional power resources they were relying on. Notwithstanding, in December 2017, a transnational group of union-related pilots, the European Employee Representative Committee (EERC), successfully coordinated strikes across Europe, forcing Ryanair to finally recognise trade unions. But why did an informal, transnational group of union activists succeed where all national unions across Europe had hitherto failed? This critical case study shows that the weakening of national unions does not necessarily undermine transnational collective action. Also, EU governance structures at times can provide workers with unexpected leverage that can be used to trigger transnational collective action. Hence, transnational union strength cannot be deduced from an aggregation of national power resources. It also depends on the ability of union activists to exploit peculiarities in the contradictory EU governance regime. By deciding to recognise national unions (instead of the EERC), however, Ryanair also returned industrial relations to the national level, thereby making the transnational coordination of strike action more difficult.