Recent literature argues that trade unions in restructuring service industries have responded to the challenges of the post‐industrial era by accepting different forms of labour market dualization. This article examines two case studies from Italy and Greece, in which unions adopted divergent responses to intensified market pressures unleashed by the liberalization of national telecommunications markets. In the Italian case, collective bargaining was successfully centralized, resulting in the inclusion of traditional labour market ‘outsiders’. In contrast, bargaining centralization failed in Greek telecommunications, leading to intensified dualization. These different paths of institutional change are explained as resulting from differences in ideological cleavages among unions and distinct legacies in employers’ associations.