Haymarket Riot, 1886, Harpers' Weekly (Library of Congress)

On May 3, 1886, just two days after some 350,000 workers across the nation struck to achieve the eight-hour day, Chicago police killed two people and wounded several more after violence erupted between strikers and strikebreakers at the McCormick Harvesting Machine Company. Protesting this action, anarchist August Spies held a meeting at Haymarket Square on May 4. When police forcibly dispersed the small crowd, an unidentified assailant threw a bomb that immediately killed one policeman and fatally wounded six bystanders. That summer Spies and seven other anarchists were tried and convicted of murder. George Engel, Samuel Fielden, Adolph Fischer, Louis Lingg, Albert R. Parsons, Michael Schwab, and August Spies were sentenced to death and Oscar W. Neebe received a long prison term.

In 1887, Gompers joined representatives from the New York City Central Labor Union (CLU) and the Knights of Labor District Assembly 49 to campaign for more lenient sentences. They jointly sponsored a public appeal to workingmen on behalf of the condemned men. They also held a mass meeting on October 20, 1887, to denounce the verdict and the lack of a fair trial. On November 9, Gompers, James Quinn, Frank Ferrell, and Edward King went to Illinois as representatives of the New York City CLU to present Governor Richard J. Oglesby with a petition calling for the commutation of the sentences. The governor converted the sentences of two of the seven condemned men (Samuel Fielden and Michael Schwab) to life imprisonment. Of the others, Louis Lingg committed suicide before his execution, and George Engel, Adolph Fischer, Albert R. Parsons, and August Spies were hanged on November 11, 1887. On June 26, 1893, Governor John P. Altgeld pardoned Fielden and Schwab, along with Oscar W. Neebe, who had been sentenced to a fifteen-year term in prison.