The free movement of people is a fundamental principle of the European Union (EU) that has led to an increase in EU-internal migration. This study investigates the impact of increased immigration to Germany resulting from the 2004 and 2007 eastern enlargement of the EU on concerns about immigration within the German population. By merging 20 years of annual migration statistics with panel data on individual attitudes and exploiting exogenous variation in the gradual enlargement of the free movement policy, we examine the causal effects of EU-internal migration on immigration concerns. Our findings suggest that the influx of immigrants from new member states did not have a clear average effect on concerns about immigration, but increased concerns among German natives with materialist-survival values. The study provides insights into the societal division caused by opposition to immigration as part of the European integration process.