The Second International designated May 1 as International Workers’ Day in 1889.
The decision emerged from the International Workers’ Congress held in Paris in July 1889, which helped establish the Second International, an alliance of socialist and labour parties. French syndicalist Raymond Lavigne proposed coordinated demonstrations demanding an eight-hour working day.
The date was chosen to connect international action with the anniversary of the 1886 Chicago labour protests, including the Haymarket affair. The first major May 1 demonstrations took place in 1890 across Europe, the United States, and parts of Latin America.
A common mix-up is the distinction between choosing the date and formally establishing an annual observance. The 1889 congress called for the demonstrations; the first widespread observance was in 1890, and the event received further formal recognition at the Second International’s 1891 congress.