In the early 20th century, it was common for children, some as young as 4, to work in America’s factories, mines, fields, canneries, and tenement sweatshops. In 1910 children under the age of 15 made up 18.4 percent of the nation’s workforce. Outraged reformers began a campaign to end child labor in the United States. By 1915 several states had passed child labor laws. Congress twice enacted legislation, which the Supreme Court ruled unconstitutional. A constitutional amendment restricting child labor passed Congress in 1924, but the necessary number of states failed to approve the amendment. In 1938, the Fair Labor Standards Act was passed, prohibiting most children under age 16 from working in industry. Agricultural and domestic labor were excluded.