We hypothesize that incomplete integration into the workplace and society implies that immigrants are less likely to be union members than natives. Incomplete integration makes the usual mechanism for overcoming the collective action problem less effective. Using data from the Socio-Economic Panel, our empirical analysis confirms a unionization gap for first-generation immigrants in Germany. Importantly, the analysis shows that the immigrant-native gap in union membership indeed depends on immigrants' integration into the workplace and society. The gap is smaller for immigrants working in firms with a works council and having social contacts with Germans. Our analysis also confirms that the gap is decreasing in the years since arrival in Germany.