In 1889 an international federation of socialist groups and trade unions designated May 1 as a day in support of workers, in commemoration of the Haymarket Riot in Chicago (1886). Five years later, U.S. Pres. Grover Cleveland, uneasy with the socialist origins of Workers’ Day, signed legislation to make Labor Day—already held in some states on the first Monday of September—the official U.S. holiday in honour of workers. Canada followed suit not long afterward.