From the U.S. Department of Labor, History of Labor Day:

“Observed the first Monday in September, Labor Day is an annual celebration of the social and economic achievements of American workers. The holiday is rooted in the late nineteenth century, when labor activists pushed for a federal holiday to recognize the many contributions workers have made to America’s strength, prosperity and well-being.

“Before it was a federal holiday, Labor Day was recognized by labor activists and individual states. After municipal ordinances were passed in 1885 and 1886, a movement developed to secure state legislation. New York was the first state to introduce a bill, but Oregon was the first to pass a law recognizing Labor Day, on February 21, 1887. During 1887, four more states – Colorado, Massachusetts, New Jersey and New York – passed laws creating a Labor Day holiday. By the end of the decade, Connecticut, Nebraska and Pennsylvania had followed suit. By 1894, 23 more states had adopted the holiday, and on June 28, 1894, Congress passed an act making the first Monday in September of each year a legal holiday.”