Power resource approaches (PRA) remain heavily focused on the national level and have failed to keep apace with contemporary, yet significant, political and economic developments. Whereas the European integration project has put unions on the back foot, it has also resulted in transnational labour activism (TLA), which remains under-theorised by PRA scholars. By drawing on different literatures and two complementary comparative studies, this chapter assesses TLA and ‘scale’ through a PRA lens. We analyse power resources in different sectors by comparing two European Citizens’ Initiatives, one successful and one unsuccessful, and union recognition struggles within Ryanair. Whereas national power resources failed, supranational power resources proved critical in explaining the airline’s decision to recognise unions. We find that TLA is also shaped by structural conditions, i.e. the prevailing mode of European integration. Here, we differentiate between ‘horizontal’ and ‘vertical’ integration and place an emphasis on the interplay of power resources that exist at different scales in explaining successful outcomes.