Labor unions

I assume in the US? I have run many union shops, some are wonderfully collaborative and others are completely destined for self-inflicted failure. I'd spend a lot of time talking and listening to the union leadership and the local HQ guys. There are North American unions (un-named) that really don't mind driving a company into bankruptcy every year or so, just to make a point and let the industry know they're not messing around. Others will be driven by local idiots who are just dangerous, like a kid playing with a loaded gun. Enough conversations should let you know where they are on that spectrum. You have as much chance at changing them with equity as changing the nature of a rattlesnake. Bankruptcy courts are littered with formerly profitable ESOP companies.
But, other union situations are amazing and an absolute benefit to the (very wise and crafty) entrepreneur. You don't end up there by accident, it takes avoiding toxic situations and having a plan for the healthy ones. Good luck

Also, one thing to consider is if the union is an internal union created by the company or an outside more traditional union.