On May 26, 1937, workers of 3 major independent steel mills—Republic Steel, Youngstown Sheet & Tube, and Inland Steel—voted to strike over low wages and poor working conditions. Once the workers walked out and formed picket lines, the companies brought in strikebreakers—”scab” labor—to run the factories. That decision did not go well for either side of the dispute in the Ohio mills.
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Four days later in Chicago police opened fire on a crowd of unarmed strikers and sympathizers, killing 10 and wounding 30 (including 2 women and a child), in an event known as The Memorial Day Massacre.
Source: Santa Cruz News, June 7, 1937 via California Digital Newspaper Collection, Center for Bibliographic Studies and Research, University of California, Riverside