In what way do the corporatist and authoritarian legacies that modelled some Latin American labor institutions influence the opportunities for and restrictions on organizing workers in a new context? To what extent did institutional designs, together with other economic and political factors, influence the characteristics that currently distinguish the union organizations in the countries of the region? Taking into consideration the existence of a broader debate about the consequences of globalization and political democratization for unions, the contribution of historical institutionalism and previous research, in this Article I compare the institutional and organizational dynamics of unions in four countries with authoritarian legacies and corporatist traditions (Argentina, Brazil, Chile and Mexico). The Article argues that in spite of these shared traditions, the differences in the institutional designs — which have scarcely been considered in the specialized literature — have historically imposed distinctive features on the associational power of workers and unions. These features not only persist to the present day, but also translate into dissimilar trajectories of the labor movement and opportunities for organizing workers in the last decade.