During the early 1900s, many Mexican immigrants worked in coal mines in New Mexico, Colorado, and Arizona. Wages for these jobs were very low, and the working conditions were bad. Typically, workers were paid only by the amount of coal they brought out of the mine. Tasks like laying tracks for coal cars and shoring up tunnels were essentially performed by immigrants for free; mine owners reasoned that these projects were simply "part of" making the coal accessible for extraction.

In 1913, Mexican workers were involved in one of the worst labor-management conflicts of the twentieth century. In September of that year, the United Mine Workers of America began a strike against all coal-mining companies in Colorado. The three largest companies were the Rocky Mountain Fuel Company, the Victor-American Fuel Company, and the Colorado Fuel and Iron Company, owned principally by the "Robber Baron" John D. Rockefeller.

United Mine Workers logo

On April 24, 1914, the Colorado National Guard and armed operatives from the Colorado Fuel and Iron Mines company attacked the Ludlow tent colony, which consisted of 1,200 striking miners and their families. The colony included hundreds of Mexican immigrants, and about two dozen people were killed. Among the dead were two women and eleven children, who either burned to death or were suffocated.

The Ludlow Colony after the massacre

In retaliation for the Ludlow massacre, the miners attacked dozens of mines and engaged in open gun battles with the Colorado National Guard. Eventually, 200 people would die as a result of the strike and the massacre. The House Committee on Mines and Mining investigated the incident. The Committee's 1915 report helped to promote child labor laws and legislation mandating an eight hour work day.