Existing studies on voting cohesion in the European Parliament focus on the conflict between national delegations and European Party Groups. Yet, both principals hold conflicting views in no more than 11 per cent of the observed votes. The reasons for this high level of observed harmony are ideological cohesion and the fact that group leaders
frequently rely on the disciplining capacity of national delegations. Therefore, they coordinate their amendment activities with all major delegations. As a result, we find that
MEPs’ loyalty to support their own group’s amendment depends on their national party’s power within their group. We argue that this power depends on the party’s control over
their MEPs which, at least partly, is a result of the applicable electoral system. The lower a party’s control over their MEPs, the lower its members’ loyalty to their own group’s amendments. This finding qualifies the existing literature on voting cohesion in the EP. Moreover, this effect depends on the identity of the RCV sponsor. Specifically, our findings
provide evidence that party groups who call the roll over their own amendments can reinforce the loyalty of MEPs from weaker delegations. This result confirms previous findings
according to which MEPs who are independent from their own national party are less likely to defect on their European Political Group.
