I was looking at a Pulitzer Prize photo gallery, and the 1942 Photo was from a strike going on at the Ford Plant in early 1941. This, of course, predated American entry into the war, but it nevertheless got me wondering how Unions, Workers, and the Labor Movement, generally, dealt with the war. Was there some sort of agreement, official or otherwise, to put serious matters on hold in light of the exigencies of the war effort? What sort of collective bargaining activities, if any, continued during that period, and how successful were they?
And how soon after the end of the war did things return to 'normal'? Or even, depending on how things went in the above questions, was there long term effects of the war years on how labor relations continued in the US?
The short answer is that the government intervened even more heavily in labor management relations than it had even under the 1935 NLRA (which still forms the basis of most modern American labor law). A new agency, the National War Labor Board, not only directly mediated (and arbitrated) labor disputes, it also ran wage controls across various industries (similar to how the Office of Price Administration issued price controls).
I cannot really stress how inconceivable this standard is to a modern audience. The federal government directly set price caps on most goods as well as labor (and then rationed them as well, if you could consider the exemptions and denial of service for certain skilled labor rationing).
These standards generally increased the ability of unions to win organizing campaigns and union density was significantly higher after the war, even though it had been steadily rising since 1935. Because of the wage caps set by the NWLB, many of these unions sought other concessions from employers instead of increased wages (which would have been illegal), such as health care, vacations, and pensions. This process is the partial genesis of why American companies often have employer sponsored health care.
The Roosevelt administration also intervened forcefully to uphold rulings of the NWLB. Sewell Avery, the CEO of Montgomery Ward (a mail order/department store retailer like Sears), was arrested by federal troops when he refused to follow the orders of the NWLB. Similarly, the wage controls issued by the NWLB sometimes meant a paycut, which caused a major strike of coal miners in 1943. This strike resulted in the Smith Connally Act, which allowed the federal government to nationalize war related industries affected by strikes or lockouts. Roosevelt vetoed that bill (which was overridden), but did seize the mines and negotiate a settlement with the United Mine Workers (after threatening to draft them). Another note is that Smith-Connally prohibited union contributions to federal elections, prompting the CIO to form the first Political Action Committee (PAC) that we still see today.
Finally, I'd like to touch on race and integration. Many defense industries (which was a broadly applied term) were subject to Executive Order 8802 and subsequent expansions, which prohibited employment discrimination in defense industries. Think of this as a proto-Title VII. These efforts did not always go over well. There were several instances of wildcat strikes by rank and file union members in response to federal attempts to integrate their shops. In 1943, there was a massive race riot in Detroit which required federal troops to put it down. In 1944, Philadelphia transit workers went on strike to protest the hiring of black motormen on streetcars. Roosevelt actually did invoke Smith Connally, seized the transit system and operated it with federal troops.
The New Deal and WWII set the tone for federal labor law and the political economy of labor management relations for the next 40 years. There was a general status quo which existed after the war (and after some stuff related to the UAW and merger of the AFL and CIO which I don't have time to go into) which lasted until 1968 and then began to fissure. The current labor environment is a legacy of the Reagan administration, which hews too close to current politics for me to effectively cover here.
Edit: OK, so this didn't end up being very short. I also didn't cover another massive issue which was the entry of a significant number of women into the labor force. The actual TL;DR there is that while a massive presence of women didn't last, it did provide effective examples for the expansion of civil rights laws covering sex as a protected class which started in the immediate post-WWII era and culminated with the Equal Pay Act and Title VII in the mid-1960's (and then continued until now, but I digress).