The first federal law regulating child labor in the United States was the Keating-Owen Act of 1916, which prohibited the transportation of goods across state lines if they had been produced by children under the age of 14, or by children between the ages of 14 and 16 who worked more than eight hours a day or six days a week. However, this law was later declared unconstitutional by the Supreme Court in 1918. It wasn't until the Fair Labor Standards Act of 1938 that comprehensive child labor laws were established, prohibiting the employment of children under 16 in most industries and setting minimum wage and maximum hour standards for workers.