This article examines the stances of Polish trade unions on EU enlargement, intra-EU labour mobility and EU service market liberalization. It shows that, despite the liberal rhetoric embraced by mainstream media and successive Polish governments, the country’s labour organizations did not lend their support to the logic of low-cost competitiveness. The article accounts for this stance by referring to the insider-outsider theorem. It argues that whereas transnationally mobile workers and self-employed individuals (the ‘outsiders’) could make use of short-term cost advantages, the domestic workforce (the ‘insiders’) benefited from the gradual improvement of employment conditions in Poland and their convergence with western standards. The desire to cater to the interests of the insiders made the unions reject social dumping and defend the west European social ‘archetype’ to which their countrymen aspired.