It was in the aftermath of a bombing at a labour protest against the Chicago police in 1886 that it was decided to mark May 1 as International Workers' Day.
The origin dates back to the 19th century after the labour and trade movements went up in the US. Labour Day is a public holiday in most countries across the world.
A peaceful rally was being carried out on May 4 1886 at Haymarket square in Chicago to support workers who were striking for work hours not more than eight hours. They were also protesting the killing of several workers by the police the previous day.
During the protest, an unknown person hurled a bomb at the cops as they were trying to quell the protesters. Gunfire ensued after the bombing and seven police officers an at least four civilians were killed. The incident is remembered as the Haymarket affair, or the Haymarket massacre. The place in Haymarket Square where the incident happened was designated a Chicago Landmark in 1992.
India marks May Day as "Antarrashtriya Shramik Diwas".