Labor unions flourished for a number of reasons: abysmal working conditions, a lack of concern for workers' safety, low pay and nonexistent benefits, and a 10-to 12-hour workday. The Knights of Labor, one of the strongest unions, focused on achieving an eight-hour day. After a worker was killed at a labor rally, the crowd broke out in violence. Firing into the crowd, the police killed four workers. The long-term effect of this riot was widespread fear of unionism and a delay in the acceptance of the eight-hour day.