This article discusses the implications of EU enlargement eastward for the so-called 'European social model' and the 'Europeanization' of industrial relations. After considering the standpoints of EU bodies, it supports an alternative 'agency-based' perspective. A deeper analysis of the Polish case reveals that not only has enlargement an impact on industrial relations, but conversely industrial relations has a considerable impact on enlargement. A particular asymmetry is detected. In the West, employers strongly promote enlargement and unions (especially in some countries) are increasingly sceptical; in the East, the opposite is the case. This asymmetry increases the risks of American-style fragmentation of European industrial relations.