Excerpts from Books and Wikipedia
"In Chicago a strike against the McCormick Harvesting Machine Company turned ugly when strikers attacked blacklegs who tried to cross the picket lines. On May 3 the police intervened, and at least one striker was killed and others were injured. There was a peaceful protest against police brutality in Haymarket Square the next day, but when the police moved to disperse the crowd, someone threw a bomb, killing one of the policemen. They police opened fire and a riot erupted that ended with six more policeman dead and around 60 injured, along with an unknown number of demonstrators. Eight labor leaders were convicted of conspiring with a murderer, despite the absence of evidence. They were all socialist or anarchist agitators and mostly foreign born, which evidently weighed with the jury. Four of the convicted were hanged in November 1887, and another killed himself. The remaining three were pardoned in 1893. By that time, however the American Federation of Labor had been founded and labor unions would become an accepted part of the US economy and politics." [Furtado: 1001 Days]