Author(s) Fumi Ikeda Keywords organizational votes, political parties, elections, labor unions, the Democratic Party of Japan Abstract 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. Author(s) Bio Fumi Ikeda is a PhD student at Chuo University, Tokyo, Japan. DOI: 10.1017/jea.2018.30