Thanks for pointing out that May Day is a worldwide celebration of the martyrs of Haymarket Square in Chicago and the fight for the 8-hour day.
Unfortunately, you were a bit confused on the details. The martyrs were the union leaders who were executed after being falsely convicted of planning/throwing the bomb that killed the police officer. Many observers have blamed the authorities themselves for the bomb as a pretext to discredit the labor movement and crack down on its leaders.
Have an 8-hour day? Thank a union member.