Poor writing
This movie suffered from some pretty flawed storytelling. Just a couple of examples:
1) He beats up the union president's muscle and then slaps the president around. That's it? The guy never retaliates? He just gives up for life? Never tries to get the drop on Greene? Just poor fiction. It didn't happen like that of course because that would be ridiculous.
2) The FBI gets him a BS sentence but he never has to feed them any info? And they tip him off about a rat in his ranks? Why? Why would the FBI have a one way relationship that they don't benefit from? Again, it didn't happen that way. Just poor fiction. In real life, he fed the FBI plenty of information--none that would mess his own spot up or his friends' but he definitely fed the FBI tons of information.
Also, they portray him as some sort of worker rights guy, when it is well known that he was raising dues and otherwise ripping the small guys off. He made his bones on the backs of hardworking working men. He was a piece of crap.