Most literature on European constitution-building models member-states as unitary actors which monopolize bargaining power. However, recent advances in the literature on intergovernmental conferences (IGCs) demonstrate that both supranational actors and parliamentary domestic actors may influence treaty outcomes (Hix, 2002; Hug and Konig, 2002). We examine different potential sources of power available to parliamentary actors at IGCs through the use of spatial bargaining models. Using both open rule and closed rule models, we explore the power of the European Parliament (EP) and member-state parliaments at the Amsterdam IGC leading to the Treaty of Amsterdam. We empirically determine which actors have agenda-setting rights and if and when domestic constraints matter. Furthermore, we examine whether this influence differs across the different types of issues discussed at the IGC. Our findings demonstrate that supranational actors such as the EP may have some agenda-setting power over some types of issues. Because the EP often has very similar preferences to the European Council President, however, it is difficult to determine which actor actually has first-over advantage. In general, the EP is weak: hawkish domestic parliaments, on the other hand, can be a source of power for member-state negotiating teams. We find evidence that domestic constraints may even be a more important source of power than first-mover rights. Member-states that have both a hawkish parliament and are moderately divided tend to perform the best. Highly divided governments, however, perform poorly.
