Increases in the number of jobs for part-time workers has had little impact on the rate of unionisation for part-time workers, the majority of whom are women. The argument run by union officials in Japan is that women, and thus part-time workers, are not interested in industrial issues. This study explores an alternative explanation which is that union officials and "core" male workers are excluding women and part-time workers in order to protect their own privileged position. Whilst it is acknowledged that the organisational structure of enterprise unions makes it difficult to incorporate the needs of part-time workers, it is the attitudes of "core" male workers and union officials to women as paid workers that is the major hurdle to the non-unionisation of part-time workers. For women and part-time workers there is no power in the union.