It is not just corruption. It's laziness. Every union I have worked with (2 I worked in, 1 I managed union workers) has been in favor of the lowest common denominator. They spend time squabbling about the worker that barely get by doing the bare minimum but knows the rules. Meanwhile the really hard workers get fired for one time mistakes and the really good workers don't make as much as they should because of the guys that are barely skating by.
Unions don't do what they used to. They used to make management know that they needed to cooperate. Now it is not how they work together.