The paper analyses the impact of the reach of communist parties, the degree of political activism, personal attributes of workers, and industrial characteristics on the individual decision to unionise for Indian non-agricultural regular workers using micro data from the 2004-05 Employment and Unemployment Survey, NSSO, linked to state-level factors. A notable result is that the reach of communist parties has considerable effect on unionisation probability. Moreover, it seems that mere existence of communist parties in a state also facilitates unionisation to some extent. State-level political activism and unemployment rate also influence the individual decision to be unionist. The paper concludes also that workers 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.