Interest groups and other organizations are crucial vehicles for voter mobilization, but variations in their capacities are not well understood. To clarify the ways in which vote mobilization capacities vary, I analyze vote mobilization in two private-sector industrial unions supporting the Democratic Party of Japan (DPJ). The Japanese Federation of Textile, Chemical, Food, Commercial Service and General Workers’ Union (UA Zensen), has a very large membership but mobilizes few votes. The Confederation of Japan Automobile Worker's Unions (JAW), on the other hand, has fewer members but mobilizes more votes. In this article, I argue that unions whose constituent units operate company towns are most successful in mobilizing votes. Organizational capacity –independent of membership size – matters in the electoral arena. Using data from House of Councillors elections, I show that those industrial unions that include many enterprises with company towns have advantage in voter mobilization.
