Final answer:
A careful rereading of the excerpt reveals that the ILGWU was predominantly made up of female workers, as indicated by the distinction between 'union men' (observers) and 'these girls' (active participants).
Step-by-step explanation:
A careful rereading of the excerpt from "We Shall Not Be Moved" would allow a reader to understand that the ILGWU (International Ladies' Garment Workers' Union) was primarily composed of female workers. This is based on the statement in the quote that "these girls" are doing something remarkable that even men might not be able to endure. The term "union men" further reinforces the distinction between the male officials and observers, and the primarily female membership who were active participants in the picketing described.