A result of the Haymarket Riot was repression of union activities and the explicit disassociation of the mainstream labor movement from anarchists and radicals. The Haymarket Riot was a labor protest in Chicago on May 4, 1886, that turned violent when someone hurled a bomb at the police.
The rally took place in Chicago's Haymarket Square as a part of the campaign to secure an eight-hour workday. Though the protest was generally peaceful, at the end of the day an unknown assailant lobbed a dynamite bomb at police, who responded with random firing into the crowd. Seven policemen and between four and eight protesters died. The incident sparked widespread suspicion of political radicals, labor leaders and immigrants, and the police arrested eight men, the "Chicago Eight," who subsequently received death sentences even though some were not even present at the event.
Some Americans viewed the Haymarket Riot as another reason to be suspicious of organized labor, and the Knights of Labor, the organization that received blame for the event, saw a decline in membership. However, the incident galvanized other sectors of the labor movement. The Chicago Eight became martyrs for the cause, and while the unions publicly repudiated radical politics, they continued to agitate for better working conditions. In July 1889, the American Federation of Labor, one of the largest labor organizations in the United States, dedicated May 1 as International Labor Day, or May Day, in honor of the Haymarket affair.