Many of the workers were already members of the American Railway Union (ARU), led by Eugene V. Debs, which supported their strike by launching a boycott in which union members refused to run trains containing Pullman cars. The strike effectively shut down production in the Pullman factories and led to a lockout. Railroad workers across the nation refused to switch Pullman cars, and subsequently Wagner Palace cars, onto trains. The ARU declared that if switchmen were disciplined for the boycott, the entire ARU would strike in sympathy.
The boycott was launched on June 26, 1894. Within four days, 125,000 workers on twenty-nine railroads had quit work rather than handle Pullman cars. Adding fuel to the fire the railroad companies began hiring replacement workers (that is, strikebreakers), which only increased hostilities.
On June 29, 1894, Debs hosted a peaceful gathering to obtain support for the strike from fellow railroad workers at Blue Island, Illinois. Afterward groups within the crowd became enraged and set fire to nearby buildings and derailed a locomotive. Elsewhere in the United States, sympathy strikers prevented transportation of goods by walking off the job, obstructing railroad tracks or threatening and attacking strikebreakers. This increased national attention and fueled the demand for federal action.
The strike was broken up by United States Marshals and some 12,000 United States Army troops, commanded by Nelson Miles, sent in by President Grover Cleveland on the premise that the strike interfered with the delivery of U.S. Mail, violated the Sherman Antitrust Act and represented a threat to public safety. The arrival of the military and subsequent deaths of workers led to further outbreaks of violence. During the course of the strike, 13 strikers were killed and 57 were wounded.