Mr. Monk Meets Dale the Whale - S1-E4
Revealing mistake: When Monk is showing how Dale and his Doctor murdered the judge one can see that the knitting of the right chair is already cut to ensure that the policeman will fall through it when he later steps on it.
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