The 1905 Chicago Teamsters' strike was a sympathy strike and lockout by the United Brotherhood of Teamsters in the summer of 1905 in the city of Chicago, Illinois. The strike was initiated by a small clothing workers' union. But it soon spread as nearly every union in the city, including the Teamsters, supported the job action with sympathy strikes. Initially, the strike was aimed at the Montgomery Ward department store, but it affected almost every employer in the metropolitan region after the Teamsters walked out. The strike eventually pitted the Teamsters against the Employers' Association of Chicago, a broad coalition of business owners formed a few years earlier to oppose unionization in Chicago.

The strike was a violent and deadly one. Riots erupted on April 7 and continued almost daily until mid-July. Hundreds and sometimes thousands of striking workers and their supporters would clash with strikebreakers and armed police each day. By late July, when the strike ended, 21 people had been killed and a total of 416 injured. It was the second-most deadly labor dispute in 20th-century American history, surpassed only by the East St. Louis Riot of 1917.

Court testimony in late summer revealed that various businessmen (including the general manager of Montgomery Ward) had taken bribes to lock out their workers. The testimony also revealed that union leaders had asked for and received bribes to end their strikes. The testimony significantly undercut public support for labor unions, and the strike quickly collapsed. The strike is generally considered to have lasted 103 days from the date the Teamsters entered the fray on April 6 until its conclusion on July 19, when most unions voted to withdraw from the dispute.

The strike is considered one of the most important of early 20th century American history because of its violence, the strength and depth of inter-union solidarity, and the way it dramatically weakened public support for unions nationwide.

The Employers' Association of Chicago (the EA) was formed in 1902 during a strike against telephone equipment manufacturers.

In January 1902, Brass Molder's Union Local 83 struck Stromberg-Carlson and Western Electric, seeking to win the closed shop in collective bargaining negotiations. The employers locked out the workers and brought in strikebreakers. Union members began to physically attack the strikebreakers. On May 7, 1903, the union struck the Kellogg Switchboard & Supply Company. Kellogg Switchboard, too, locked out its workforce and hired strikebreakers. The Teamsters Joint Council of Chicago, a city-wide organization of all Teamster locals in the Chicago area, began a sympathy strike on June 24, 1903. The three employers sought injunctions against the sympathy strike, which they won on July 20, 1903. The Brass Molders' strike collapsed soon afterward.

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