In the years and months prior to the May 2004 enlargement of the European Union, transitional periods of two to possibly seven years were imposed upon free movement of labour for immigrant workers from new (Eastern European) member states by a majority of ‘old’ member states. This article aims to scrutinize fear of mass migration from new member states by examining where (ir)rationality and political opportunism meet in the perception of this particular flow of labour migration as a cause for contemporary moral panic. To this purpose, the article starts with embedding the notion of fear of mass migration in literature on moral panics, risk society and the ‘othering’ of economic migrants as strangers and folk devils. By means of a case study narrative of the decision-making process on the free movement issue in the Netherlands, it is subsequently demonstrated that ‘politics of fear’ are deeply rooted in the uncontrollability of mobilities of an unknown magnitude and an uncertain impact on, for instance, domestic labour markets. Beyond rationalizable concerns of job loss, however, labour migrants from new member states are also feared as threats to borders of morality and identity in Western European societies. The narrative's results are placed within a wider context of current boundary drawings with regard to migration in the enlarging European Union.