In the Navy, we called a public sector union a 'mutiny'.
You'll be hard pressed to find a large police union that isn't Democratic, much like most unions.
At least on campaigns I've worked on they tend to endorse what comes out as the more 'conservative' candidate because it's all realpolitik: the candidate which promises the most police friendly policies and who has the best relation (and thus would be friendliest in office to) police, fire, ems, whatever group leaders.
Which are usually considered the more 'conservative' or policy friendly.
I've been the guy in uniform who turned up to negotiate a peaceful settlement to a transport dispute. I'm not sure why the inspector picked me to go inside the picket with him, but once there we both ended up dealing with the union. My starting points were "you want an outcome, some of this is private property, some is a road under the traffic act, but irrespective, nobody wants an injury" (trucks driving over people in the picket seemed distinctly possible) and "I'm a union guy"- which an inspector is not really (they have a separate commissioned officer union which .. is. .not like a union )
We didn't move anybody in the picket. Management acknowledged the petition. Business resumed later that day and no-one got runover. Over the next 18 months there were investigations, in various states including ours, that identified breaches of transport acts, OHS etc, by some of the contracting companies- and a couple of directors got fined. And going on, general issues with trucking law enforcement , fatigue management etc had an impact on normalising the laws across the states. (ie the transport unions had a valid point about problems in the industry)
So I'd say, don't expect police to go heavy against unions, you may be disappointed. 15 years exp.
YMMD outside Australia
"fires" refers to termination of employment, not firemen.
My grandfather was child laborer in the coal mines in Illinois and saw scabs get killed when he was barely a teenager.
When workers have had to literally, physically fight and sometimes die for what we now consider to be workers rights, who were they fighting? who killed them? Often it was the police.