Which organization chose May 1 as an international workers’ day in 1889?

The Second International chose May 1 as an international workers’ day in 1889.

The decision was made at the founding congress of the Second International in Paris. Delegates supported a worldwide demonstration demanding a legal eight-hour working day, linking their campaign to a planned labor protest in the United States.

May 1 was also connected with the large demonstrations in the United States in 1886 and the Haymarket affair in Chicago. The date therefore acquired both a practical organizing purpose and a symbolic connection with the international labor movement.

The Second International was a coalition of socialist and labor parties founded in 1889. It should not be confused with the International Labour Organization, which was created later, in 1919, as part of the post-World War I international system.