International Workers' Day

International Workers' Day, also known as Labour Day in most countries and often referred to as May Day, is a celebration of labourers and the working classes that is promoted by the international labour movement and occurs every year on May Day.While it may belong to a tradition of spring festivals, the date was chosen in 1889 for political reasons by the Marxist International Socialist Congress, which met in Paris and established the Second International as a successor to the earlier International Workingmen's Association. They adopted a resolution for a "great international demonstration" in support of working-class demands for the eight-hour day.

Source: Wikipedia