This article compares coordinated collective bargaining in Sweden and Denmark after centralized bargaining. Existing theories — power resource and cross‐class alliance theory — seem capable of explaining the transition from centralized bargaining to pattern bargaining system. However, they do not explain the internal stability of bargaining coordination once established. This analysis stresses the role of mediation institutions of both countries for solving collective action problems in pattern bargaining by pegging other settlements to the manufacturing labour cost norm. Mediation capabilities, however, differ, which is reflected in more frequent defections in Sweden than in Denmark and thus a more unstable bargaining coordination. These differences have substantive consequences for bargaining outcomes in the two countries.