In recent years Latin American countries have enacted sweeping privatisation measures and major trade, financial and tax reforms, but they have moved much more slowly to reform their pension systems and labour laws. This pattern of reform partly reflects differences in the intensity of organised labour's opposition to the reforms. Organised labour has undertaken greater efforts to block labour law reforms and, to a lesser extent, pension reforms, because these measures impose severe losses on more unions than other types of reforms. These greater efforts, moreover, have had significant effects on policy outcomes. The article shows how organised labour reacted quite differently to various types of market-oriented reforms in Argentina and Mexico in the 1990s, and describes how the reaction of the unions helped shape the fate of the reform proposals.