Do political attitudes influence the likelihood of employees being members of a trade union, and to what extent is this the case in the Nordic countries with their high aggregate levels of membership? In this article, I address these questions using European Social Survey data from 2012. The results show that left-wing political attitudes have the most impact on the likelihood of trade union membership in Sweden and to a lesser extent in Denmark. In Norway and Finland, there is no statistically significant impact. I argue that the impact of left-wing political attitudes on unionization in Sweden and Denmark reflects a conception among employees that trade unions are normative organizations.