Party cohesion in legislatures is a topic of longstanding concern to
political scientists because cohesion facilitates democratic representation. We
examine the cohesion of transnational party groups in the European Parliament,
which is part of the EU’s bicameral system, and study the oftentimes competing
pressures to which MEPs are subject from their EP party groups and national
governments. Our explanation focuses on the conditions under which MEPs take policy
positions that differ from those of their party groups. We propose that
national governments lobby their national MEPs more intensely on issues of high
national salience and on which they are in a weak bargaining position in the
Council. The analyses offer a unique approach to the study of party cohesion
that is based on the policy positions taken by each national delegation of MEPs
in each of the three main party groups and national governments on specific
controversial issues.