Some leftists argue that police are essentially an extension of state power, and so not labor in the traditional sense. To have a Union that protects state power only serves to doubly oppress the people state power is used against. These people then argue that police unions are a corruption of the idea of unions, and should not exist. Laborers should have Union protection, but not the state.

I should say I’m not too well versed in this argument, so this is my vague recollection of its high level points.