There is a debate in international relations on how, when, and why international institutions influence domestic policy. This article contributes to this debate by looking at the influence of the World Trade Organization (WTO) on the European Union's (EU) Common Agricultural Policy (CAP). It shows that the transfer of authority to international institutions may transform an external factor into a permanent influence on domestic policy. The transfer of authority in agriculture to the General Agreement on Tariffs and Trade (GATT - now included in the WTO) in 1994 led to the introduction of a dormant clause on export subsidies in all subsequent EU CAP regulations. This clause provided the legal foundation for the 2015 EU decision to remove export subsidies. Multilateral pressure (i.e. the demands of third countries in GATT/WTO negotiations) is not the only determinant of CAP, but it is important, and affected by the GATT/WTO having authority on agriculture.