This working paper explores the processes in which accession to different regional blocs has affected the ways the state interacts with societal actors, along with the interest representation and mediation models in both member and accession countries. Focusing on Turkey and Mexico, two upper-middle-income countries situated on the fringes of major powers and integrated into the regional blocs led by those, the paper examines the differential impact of the European Union (EU) and the North American Free Trade Agreement (NAFTA) on the organization and mediation of business interests; the ways in which these interests are incorporated into policy-making; and the processes of social dialogue. Taking into consideration the fundamental differences between these two regionalisms, it looks into both direct and indirect mechanisms with respect to the influence of regional-level actors on domestic actors and institutions. Maintaining that the impact of regional blocs cannot be easily isolated from that of international, transnational actors and processes, the paper scrutinizes the respective roles of international actors and transnational networks which, at times, have become more influential than the regional blocs in bringing about major institutional changes at the domestic level. Thus, it sheds light on processes of comparative regionalization and their varying influences on distinct polities, which is usually combined and even furthered or, rather, obstructed by the influences of transnational, international and global forces, along with domestic actors and institutions.