On the night of May 4, 1886, a crowd of several thousand workers gathered for a public rally at Haymarket Square in Chicago. Because the crowd was smaller than expected, it was moved to a different location a short distance away, to Desplaines Street and Crane’s Alley behind the Crane Brothers metal products factory.
The rally had been called by the International Workingmen’s Party of America and its two leading organs in Chicago, the Alarm and the German-language Arbeiter-Zeitung.
A day earlier, at least two workers had been killed in a violent confrontation with police at the McCormick Reaper Works on Blue Island Avenue. The workers had been locked out since February by the owner, Cyrus H. McCormick, Jr., scion of the famous inventor, who had brought in 300 Pinkertons to escort the scabs. These were, in turn, reinforced by hundreds of police.
On May 1, the first May Day, more than 300,000 workers nationwide, including 40,000 in Chicago, walked off the job in support of the demand for an eight-hour day. While the Eight-Hour Day Movement was led officially by the Federation of Organized Trades and Labor Unions of the US and Canada, the immediate forerunner of the American Federation of Labor in Chicago, it was under the leadership of the anarchists, in particular, those associated with the Alarm and Arbeiter-Zeitung.
http://www.wsws.org/articles/2009/may2009/hay1-m11.shtml