Not just actors, but pro athletes as well. Unions have been tremendously good for them, forcing owners and leagues to commit to a specific guaranteed revenue split with players. It has not prevented rewarding of outstanding individual performance or even individual contract negotiation (just like actors). Some rules are set by by the union, including at least minimum pay, possibly maximum pay (in sports that have salary caps, it's to promote competitive balance, which acting doesn't have to worry about). But you can still negotiate quite a bit within the allowed bounds.