On Memorial Day, May 30, 1937, between 1500 and 2500 people gather for a picnic lunch, speakers, and songs in South Chicago, in support of workers striking against companies that had not signed onto a recent landmark labor deal between unions and corporate giant, U.S. Steel. As workers and their families march, unarmed, towards the gate of the Republic Steel Company, a line of about 300 police officers — supplied by the company with tear gas and clubs — opens fire. Forty people are shot, over 90 injured, and ten die.

Initial news coverage frames the crowd as a violent threat to social order, and portrays the police as acting in self-defense. No policemen are ever prosecuted for the killings.

After almost a decade more of violence nationwide, the steel industry will be completely unionized.