Like do they ever support breaking up their employers? I'm pretty sure I've seen some unions take an anti-merger stance on occasion, but I'm unsure if they've taken a more aggressive stance against their employers... I suppose it would be easier for unions that aren't specific to a company. Industry wide unions.
I'm only wondering about it because smaller companies (of the "traditional" the only thing that matters is profit, shareholders, and the C-suite variety) would be easier to bully.
(I did a quick search, but only stumbled across conservatives complaining that unions should have anti-trust applied to them. I'll try to do more searching later.)