Labor Day is a United States federal holiday observed on the first Monday of September annually. The day celebrates the American labor movement and the contributions and achievements of the American worker. Most of the world celebrates Labor Day as International Workers Day also called Workers Day or Labour Day on May 1st each year. The date for the global date was based on the Haymarket affair which occurred in Chicago on May 4, 1886 as a conflict between the police and workers where 8 people were killed. For many countries in the Northern Hemisphere May Day is also on May 1 and for them the day celebrates the coming of spring and the Labor movement together in one day.