This paper analyzes the impact on individual decisions to unionize of several factors: the reach of communist parties, the degree of political activism, personal attributes of workers, and industrial characteristics. The workers examined are Indian nonagricultural regular workers, using micro-data from the 2004–5 Employment and Unemployment Survey conducted by the National Sample Survey Organisation, linked to state-level factors. A notable result is that the reach of communist parties has considerable effect on unionization probability. Moreover, it seems that the mere existence of communist parties in a state also facilitates unionization to some extent. State-level political activism and unemployment rate also influence the individual decision to join a union. The paper concludes also that a worker's gender, marital status, ethnic background, employment status, experience, occupation, sector of employment, establishment size, and type of industry remain important in the determination of union membership.