International Workers’ Day (also known as May Day) is today.

It is a day that commonly sees organized street demonstrations and marches by working people and their labor unions throughout most of the world.

May 1 is a national holiday in more than 80 countries. It is also celebrated unofficially in many other countries.

International Workers’ Day is the commemoration of the 1886 Haymarket Massacre in Chicago, when, after an unknown person threw a dynamite bomb at police as they dispersed a public meeting, Chicago police fired on workers during a general strike for the eight hour workday, killing several demonstrators and resulting in the deaths of several police officers, largely from friendly fire.

This year members of Occupy Wall Street called for a General Strike today.

In the United States and Canada, the official holiday for workers is Labor Day in September. This day was promoted by the Central Labor Union and the Knights of Labor, who organized the first parade in New York City. After the Haymarket Square riot in May, 1886, US President Grover Cleveland feared that commemorating Labor Day on May 1 could become an opportunity to commemorate the riots. Thus he moved in 1887 to support the Labor Day that the Knights supported.