1892: Showdown at Homestead steel plant

By the late nineteenth century, the workers at Andrew Carnegie's Homestead, PA plant had eked out a modicum of power. They won a key strike in 1889, and in the process became a potent unit of the Amalgamated Association of Iron and Steel Workers. Still, these victories hardly erased the harsh working conditions at the Homestead mills. Nor did they mean that the Carnegie Company was pleased with or readily recognized the union. 

Ever mindful of Amalgamated's potentially deleterious impact on his profit margins, Andrew Carnegie looked to erode the power of the union. In 1892, the company made its move against Amalgamated, though not with Carnegie at the helm: the steel baron had departed for a vacation in Scotland, leaving the task of smashing the union in the hands of his partner, Henry Clay Frick. 

Frick took his mission all too seriously: after refusing to renew the company's contract with Amalgamated, he dug in for war, erecting a three-mile long steel wire fence around the plant. Frick also enlisted the aid of the Pinkerton Detective agency, which sent three hundred men to Homestead to ensure the plant's transition to non-union workers. 

Seven strikers and three Pinkertons were eventually killed as Andrew Carnegie hires armed thugs to protect strikebreakers in an effort to smash the union.

Amalgamated's leaders responded in kind, lining up scores of workers, as well as a good chunk of the town, to wage battle against the plant. The showdown began in earnest on July 2, as Frick halted work at Homestead until the plant was staffed entirely by non-union workers. Three days later, the Homestead affair turned bloody, as the Pinkerton agents made their first appearance on the scene. Attempting to reach the plant via the Monongahela River, the agents were met by Amalgamated's forces; the two sides engaged in a long and vicious battle that left nine strikers and seven agents dead. Despite the losses, Amalgamated's motley army was able to turn back the detectives. Sensing that they were on the verge of disaster, officials for Carnegie enlisted the aid of the Pennsylvania Government. And, on this day in 1892, the state sent a band of 7000 troops to Homestead to "restore law and order." The militia effectively squelched Amalgamated's strike: the troops helped the Carnegie restaff its plant with non-union workers and by September, the Carnegie company had resumed production. Later that November, the union conceded defeat and called off its strike; Carnegie responded by summarily firing and even blacklisting the strikers.
Source: www.history.com