there was no people to fill up the positions because thousands of men were drafted into the army. taking advantage of this situation, unionized workers across the country went on strike.
The question is in the World War 1 category; I'm not positive whether that's the war you're referring to or not. However, in general, most nations no longer maintain a large standing military force...
The labor unions did have some problems. One of which was the factionalism of many different groups who could not cooperate in order to present a truly united front against employers. Immigrants also...
Women and children worked the factories supporting the war effort (the same as in the other warring countries), the men were conscripted (drafted) into military service).