No, unions have nothing to do with being socialist or capitalist or communist. Nice trolling, though.
Unions can be good - and originally they were, here in the USA. They made sure workers had decent working conditions and weren't slaving away for pennies a day. In exchange, the union would ensure that the workers were qualified and doing their jobs and provided a pathway for technical training.
Unfortunately, they started to go too far, as these things often do. Today, too many of the USA's unions are money grabbing thug organizations that would rather burn a business to the ground than give up anything at all. Many unions are only interested in excessive compensation, keeping out competition / protectionism, and political activism.
Some unions are happy to let a business die rather than capitulate on ridiculous requests. The Hostess company is one example. The American automotive industry collapsed, in part, due to the unions. Did you know that in America, when vinyl records were used to play music on the radio, that the radio union created a position with the sole responsibility of putting the record on the turnstile? Nobody else was allowed to do that simple task of putting the record on and dropping the needle. If a sound engineer were to do it they would get in big trouble.
It's nearly impossible in some industries to fire someone because of the insane power the unions can wield - and the unions will always defend you, even if you're incompetent, have committed a serious crime, or whatever. After all, they want to ensure that there's a tradition of defending everybody no matter what, so that should the people at the top get in trouble for something legitimate...
That kind of behavior is why you see a growing anti-union sentiment in the USA. I don't know what it is like over in Europe - it may be that the unions over there are a lot more sensible.
It's very unfortunate. Unions, done properly, are an excellent thing, but greed is powerful and people are stupid. Here in the USA the unions have failed.
These days, because of the protection the Federal and State laws provide, official union organizations in general seem unnecessary. All the protections that unions fought hard for have become federal law. But, that doesn't mean a group of workers, who aren't in a legal "Union", can't just walk out anyway. If they're being abused, they should walk out and make their complaints known.