Unless you need a union, you don't want a union. They are at risk to fill up with toadies that line their own pockets and screw over the workers they're actually supposed to be fighting for (by colluding with shop management on contracts). It doesn't always happen, but it can and does in some industries (private security and boilermakers unions are known to be pretty egregious in the Midwest US). When this sort of corruption happens it's very difficult to dislodge and actually makes things worse for the workers.

There's actually a plot point in Disco Elysium about this exact problem - when you're talking to wheeling dealing Evrart Claire. Look at his character portrait closely - he was drawn to look like a grinning fat toad.