The Western Federation of Miners (WFM) was a radical labor union that gained a reputation for militancy in the mine fields of the western United States. The WFM organized miners and smelter workers in the Western Rocky Mountain states after it was created in 1893 by the merger of several miners’ unions. On several occasions battles between union members and company guards, state militia and federal troops broke out during strikes.

When Frank Steunenberg, a former governor of Idaho, was murdered in 1905, Charles Moyer, president of the union, William Haywood, secretary, and George Pettibone, a former member, were arrested and stood trial for Steunenberg’s murder. All three were acquitted.

The WFM had joined the American Federation of Labor (AFL) in 1896, but the conservative policies of the AFL caused the WFM to withdraw, and, in 1898, they attempted to organize a rival federation called the Western Labor Union.

In 1901 the WFM adopted a socialist program and, after the failure of the Western Labor Union, joined the Industrial Workers of the World (IWW) in 1905. Factionalism within the IWW led to the departure of the WFM from that organization. The WFM then rejoined the AFL in 1911. The failure of several strikes and the depression of 1914 caused damage to the union causing a decline in membership. In 1916 the union changed its name to the International Union of Mine, Mill, and Smelter Workers.

The International Union of Mine, Mill, and Smelter Workers was in turn expelled from the Congress of Industrial Organizations during the early phases of the red scare in 1948. It eventually merged with the United Steelworkers of America. The movie "The Salt of the Earth" portrays a strike by New Mexico zinc miners who belonged to Mine, Mill; many of the actors were rank-and-file members of that union.