On May 4, 1886, a labor protest rally near Chicago's Haymarket Square turned into a riot after someone threw a bomb at police. At least eight people died as a result of the violence that day. Despite a lack of evidence against them, eight radical labor activists were convicted in connection with the bombing.
Knights of Labor: An Early Labor Organization. ... The organization believed that its predecessors had failed by limiting membership; the Knights proposed to organize both skilled and unskilled workers in the same union and opened their doors to blacks and women.