The point of a Union is to prevent maximizing efficiency at the cost of workers’ quality of life. Of course the rapacious billionaires and capitalists have always hated them.
No one who is in charge of other people and incentivized to come in under budget will ever truly be an ally of the workers.

Capitalists go after unions by giving department heads incentive bonuses. As soon as a foreman makes more money if they keep costs down, the workers are in jeopardy.

This has functionally destroyed the art department in film. Production designers get more work if they come under budget, and over time, they have come to embrace AI, cutting roles and making people wear multiple hats.