U.S. labour union.
Founded in 1890, the UMWA grew rapidly under the leadership of John Mitchell (president 18981908) despite determined opposition from coal-mine operators. By 1920, when John L. Lewis took over, the union had half a million members. Lewis capitalized on the pro-labour climate of the New Deal and led numerous strikes to win fair pay, safe working conditions, and benefits. The UMWA was a mainstay of the Congress of Industrial Organizations (see AFL-CIO ) in its early years, but Lewis withdrew the union from the CIO in 1942. Unaffiliated for decades, the UMWA finally joined the AFL-CIO in 1989. The UMWA's importance declined in the later 20th century with the waning of the labour movement and the rise of alternative sources of fuel, and by the 1990s it had fewer than 200,000 members.