Police unions are not ordinary ones. Ordinary unions have to fear beatings by the police. Police unions not so much.
And police unions are an important part of brutality.
They prevent disciplining officers for brutality. They influence elections to elect pro-brutality politicians, including the 2020 election. When citizens protest police brutality, they beat protesters.
Unions can be regulated. Police unions are a breakable link in the chain of police brutality.
Police unions should be forbidden to defend members against discipline. They should be forbidden to endorse candidates or organize politically.
See also: LEOs’ Bill of Rights (https://en.wikipedia.org/wiki/Law_Enforcement_Officers%27_Bill_of_Rights), a state-level package of laws assembled by a coalition police unions, which bakes into law the must-haves for preventing terminations following use-of-force.
For example, an officer can have up to 72 hours of not being interviewed, by IA or detectives, following a use-of-force death. Gives them time to make their story solid and get other officers behind them.
In Rhode Island, police officers can be convicted of felonies in civilian criminal courts, and yet still keep their jobs after a hearing before panels of fellow police officers (per WP).