Many of the war industries had contracts with labor unions, which meant that all the workers in those industries had to be union members. So, like their male coworkers, most women employed by factories during the war years were required to join a union and pay union dues. In 1940 labor unions were generally not in favor of admitting women as members. However, as the war progressed, they grudgingly admitted women, realizing that women were needed to fill the gaps left by men who were joining the military. Yet the unions spent little time explaining membership benefits to their new female members and even less time addressing issues such as childcare, maternity leave, and time off to deal with family illness.

Between 1940 and 1944 union membership increased overall from 7.5 million to 12.5 million; female members made up 3.5 million of this total. Male union members often...