SAG. The NFL Players Union. Just two examples.
Not that I think any of this is bad since the NFL is brutal to its lowest earners, but it absolutely hurts the highest earners.
Some people experience less optimal outcomes in a union. Those people are free to resist unionization. What I don't like is the claim that, because some specific high performers can no longer negotiate as well, everybody else should shut up about unionization.
But the screenwriters guild is another example if you don't want to look for one where top performers are paid eight figure salaries.