The big issue with unions in America is our labor laws create "shop" unions, where a single specific union has to win an election at a specific work site, once they do, everyone at that work site is represented by that union (in a closed shop which I think may not even be legal anymore, but if so it's a state by state thing, only union members can even work there--but even in open shops the union can collect dues and has sole right to collectively represent you), this lead to "corrupt capture" of unions for use in more nefarious things like racketeering and pay to play schemes. The way sectoral unions work in Europe is a lot healthier, you basically have the right to join any union that represents your sector, say you're an electrician and there are 4 electricians unions, you can pick which of the four you want to join. This keeps the unions honest because they are perpetually competing for members, and if one becomes too shitty and corrupt it's easy to switch to another. Employers are legally bound to negotiate in good faith with the sectoral unions, whether they have 1 person in their company as a member of that union or 50,000.
The union system in America was largely designed by anti-union forces in a corrupt fashion that made union leaders happy in the 1940s but all but guaranteed their long term failure in America.
Public sector unions largely should not exist at all, and didn't until like the 70s or something. And for good reason--public sector employees have the strenuous protections of the civil service system, which are far and above what people in private employ have. There's lots of legally defined processes where civil servants can make sure they are treated equitably.
