I would be VERY interested in a reading list of any kind, as I have lived near Chicago, which has an interesting history with both police officers and unions.
The wikipedia article on Red Squads has many references about this ugly fact. Where I live, in Portland, the Red Squad was founded in reaction to the Depression-Era victory of labor, aided by loyal American leftists, in the West Coast dock strike. It was a part of the police department located in a separate headquarters, funded in part by private contributions, and its existence was not even admitted by the mayor for about 60 years. The Red Squads found organized crime a natural and profitable ally in wealth's struggle to limit workers' power. In the 1950's, the United States Senate Select Committee on Improper Activities in Labor and Management found organized crime working closely and routinely with local authorities in Portland and well on its way to taking over the state attorney general's office. This is where Bobby Kennedy's battle against corrupt labor unions began and gave them so much national attention, when organized crime showed that it had learned that it could corrupt Republican politicians as proficiently as it had corrupted Democratic politicians.