The celebration of May Day as a labor holiday marked by parades and red flags began on May 1, 1886. Behind the first campaign was the push for universal adoption of the 8-hour working day. In Chicago, the center of the movement, workers had been agitating for an 8-hour day for months, and on the eve of May 1st, 50,000 were already on strike. Another 30,000 swelled their ranks the next day, bringing most of Chicago manufacturing to a standstill.

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On May 4, 1886, police marched on a peaceful rally, a bomb was thrown at police, and there was an exchange of gunfire resulting in the death of 4 workers and 7 police (the police were primarily shot by friendly fire). This event became known as the Haymarket massacre, and a red scare, or moral panic about left-wind ideology, followed involving police repression and media hysteria. The reactionary attack on workers and immigrants only cemented and grew working class solidarity.

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The Chicago events figured prominently in the founding congress of the Second International (Paris, 1889)—a transnational federation uniting socialist and labor parties. The congress established the first International Workers’ Day in 1890 as a demonstration of the solidarity and power of the international working class movement. Ever since, May 1st has been celebrated globally as the international workers’ holiday.

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Because of May Day’s association with socialism, anarchism, and workers’ rebellions, President Grover Cleveland chose Labor Day (first celebrated by the Knights of Labor in New York City in September 1882) rather than May Day as the federal public holiday to honor workers. Labor Day in the U.S. is celebrated as a day of leisure and parades; May Day is celebrated internationally as a day for rallies, demonstrations, and marches for workers’ rights and solidarity.