Firms are legitimate political actors, but few empirical studies examine how firms have re-structured their political organisation to maximise the political options in the constantly evolving European public policy system — or assessed the impact of these changes on the member states' industrial relations. Based on a study of Europe's largest firms, this article explores the degree to which the creation of the single market and the strengthening of European institutions has harmonised the firms' political activity across borders, sectors and issues. It concludes that multinationals have established a sophisticated political capacity that allows them to develop new multilevel and ad hoc political alliances and that this new political co-ordination has standardised political responses across issues and altered national public policy systems.