International Workers’ Day, also known as Labour Day in some countries, is a celebration of labourers and the working classes that is promoted by the international labour movement, socialists, communists or anarchists and occurs every year on May Day (1 May), an ancient European spring festival. The date was chosen for International Workers’ Day by the Second International, a pan-national organization of socialist and communist political parties, to commemorate the Haymarket affair, which occurred in Chicago on 4 May 1886.
The 1904 International Socialist Conference in Amsterdam, the Sixth Conference of the Second International, called on “all Social Democratic Party organisations and trade unions of all countries to demonstrate energetically on the First of May for the legal establishment of the 8-hour day, for the class demands of the proletariat, and for universal peace.”
Being a traditional European spring celebration, May Day is a national public holiday in several European countries. The date is currently celebrated specifically as “Labour Day” or “International Workers’ Day” in the majority of countries, including those that didn’t traditionally celebrate May Day. Some countries celebrate a Labour Day on other dates significant to them, such as the United States, which celebrates Labor Day on the first Monday of September.