When a friend joined a local mechanics union, they made him sign a contract swearing that he did not and would not, while a union member, belong to a communist or socialist party. When I was a teamster, reaction and anti-communism ran deep with just about everyone I worked with. Because of course it did, it had to. We were the beneficiaries of an agreement between imperial capital and imperial labor. They gave us good pay and good benefits, and in exchange we didn't rock the boat. Fostered an anti-boat-rocking culture.

Sure, teamsters will still fight back whenever capital steps too far over line and threatens that agreement. But it's not for the building of a better society. It's just protecting their interests.

The job of communists in labor unions is to convince their co-workers that being part of a larger socialist workers' movement and party is good. We've had some success on that front, I think, in teachers and nurses' unions specifically. But the unions tied more to market commodity production and distribution, like teamsters and painters, are substantially and often systemically less class-concious.

And to answer your question more directly, unionized cops pissed on the Black Panthers' breakfast food for kids.