Celebrated: in the United States and Canada, on the first Monday in September, since 1882
It's not entirely clear who first had the idea to set aside a day to honor our nation's workers — not the people who run things but the people who do things, the builders and fixers and caretakers who form the vast majority of the American population. The movement began in either New Jersey or New York, pushed forward by a man named McGuire or Maguire, and you can read more about it here.
130 years after its first official celebration, most people who get this day off couldn't tell you what Labor Day is supposed to honor, or why it's more important than ever that working people have the right to assemble and negotiate as a group. The economic gap between haves and have-nots is as great, if not greater, than at any time since the Gilded Age. It was the Gilded Age that spurred the trade union movement in the United States, and I keep waiting for our current troubles to spark a union revival. It hasn't happened yet, and maybe it won't — the idea of bargaining for collective good has always sat uneasily with the American ideals of self-determination.
That said, it's not politics but simple history to point out that unions negotiated most of the benefits American workers take for granted: the 40-hour work week, health and pension benefits, paid vacations, workers' compensation, and more. (As a freelancer, I wish I had any of those things.) If unions went away, would those things go away, too? I don't want to find out.