While the examination of the international political economy from the angles of states and firms is a very important endeavour, it becomes an obstacle to theoretical and empirical clarity when it reifies their constitution and preferences and when it obscures the role and agency of other social forces such as labour unions or political parties. This chapter sets out to examine and compare the role of unions in North American and European integration and thus contribute to a broader vision of international politics and to the dialogue between international politics and industrial relations (Harrod 1997).