In which year did Chicago and some other cities of USA witness protest by the labour unions which culminated in police firing which lead to the decision to observe May 01 as Labour Day

At its national convention in Chicago, held in 1884, the Federation of Organized Trades and Labor Unions (which later became the American Federation of Labor), proclaimed that "eight hours shall constitute a legal day's labor from and after May 1, 1886." The following year, the FOTLU, backed by many Knights of Labor locals, reiterated their proclamation stating that it would be supported by strikes and demonstrations.