Yes, they have a union, but there is little accountability. Their performances are reviewed after every game and the best are awarded more and better games, plus post season games. How they still get calls wrong is beyond me, even with “big brother” in NY watching over and reviewing the calls.
The MLB Umpires are awfully good with the calls on the bases, but their ball and strike calls are questionable and inconsistent.
I won’t comment on the NBA, except they determine who is going to win.
Hockey Refs do a great job considering the speed of the game.

The biggest travesty I have ever seen was the national championship game between the Miami Hurricanes and the Ohio State Buckeyes. Miami won that game in the final seconds and the field was rushed with players and fans, even the Ohio state players were heading to the sideline-when approx, 1.7 minutes after the final play an official threw a flag and called pass interference. The field was cleared and Ohio was given the ball and 1/2 the distance to the goal-they threw a TD pass and won. There is no doubt in my mind that there was a payoff involved-does anyone ever check the bank statements of these "officials".The ability to cause the final score has become a huge incentive to make money, due to money from betting. The "official" said later that he "threw the flag after thinking if he saw pass interference or not" Its too bad no one thought to look into his personal life later too see if there was any personal gain or not.