Mr. Monk is the Best Man - S8-E13
Character mistake: At the end, after Stephanie fired the gun, Captain Stottlemeyer shows her the gun's magazine but calls it a "clip." A police captain like Leland would know the difference between a clip and a magazine and would use the right word.
Answer: The two men are trying to work out a secret deal between them without involving the union, which means the workers' interests aren't being represented and defeats the whole purpose of a union. The mayor would lose labor's support and Cusack's union troubles would just be starting.
Captain Defenestrator