The cops may have a union, but that doesn't mean they aren't the paid bitches for the man. Unions should stay away from the cops, they are the people who not only crush union members with calvary as in these pics, but have been known to shoot them dead.
But it doesn't have to be that way. That labor treats them like an enemy could help maintain cops' status as enemies of labor. They have a common ground to work from, so why not try to create an alliance?