The National Labor Union was founded on August 20, 1866, in Baltimore, Maryland. It was the first attempt to create a national labor group in the United States and one of their first actions was the first national call for Congress to mandate an 8-hour work day.

In early 1866 William Harding, who was then president of the Coachmakers' International Union, met with William H. Sylvis, president of the Ironmoulders' International Union and Jonathan Fincher, head of the Machinists and Blacksmiths Union. At that meeting they called for a formal meeting to be held August 20-24, 1866, in Baltimore, Maryland. On the first day of that meeting the National Labor Union was born. Also, on that first day various committees were created to study different issues—one of which was focused on the 8-hour system.

On the third day the committee on "eight-hours in all its respects" met and made their recommendation. In the Union’s final list of resolutions made on August 20 of 1866, was their resolution calling for an 8-hour work day, the first such national call. While this call went unheeded at the time, and the organization folded in 1873, this was only the beginning of the campaign for an 8-hour work day.

Over the ensuing decades, this idea would wend its way through the country and see the rise of Grand Eight Hours Leagues. By 1912 it made its way into the progressive campaign of Theodore Roosevelt. The slogan for the movement became "Eight hours for work, eight hours for rest and eight hours for what you will." In 1916 William C. Adamson introduced the Adamson Act. While this act was specifically aimed at railroad workers, it gave the 8-hour campaign a real boost when it was passed in September 1916. Railroads immediately protested, but in 1917 the U.S. Supreme Court upheld the law in Wilson v. New (243 U.S. 332).

The increasing power of unions along with state governments legislating working hour limits and the federal government’s expansion of the use and enforcement of the 8-hour work day, meant that the 8-hour work day become even more wide-spread. But it didn't end there. A brief push for a temporary 30 hour work week in 1933 brought on by Hugo Black& had bipartisan support and passed in the Senate on April 6, but it wasn't successful. The passage of the Fair Labor Standards Act (sometimes known as the Wages and Hours bill) gave even more protections, setting the maximum workweek at 40 hours for other industries and provided that employees working beyond 40 hours a week would receive additional overtime bonus salaries.