EU policymaking shows growing political tensions. There are signs that even the implementation process of supranational acts and programs increasingly meets domestic resistance. National annulment cases against the European Commission are a case in point. Annulment cases challenge decisions that specify how supranational policies are to be implemented nationally. This chapter asks what motivates national governments to engage in judicial conflicts with the European Commission with regard to policy implementation. Three litigation motivations are theorized: preserving financial resources, defending institutional power, and maximising political trust domestically. By analysing carefully chosen annulment actions by Spain and Germany, the chapter illustrates the empirical validity of the litigation motivations. It finds that the conceptualized motivations are indeed present in all the cases studied, though sometimes in particular combinations. Our findings help overcome functional biases in compliance research and highlight the utterly political character of national resistance to EU implementation.