Mr. Monk Meets the Godfather - S3-E5
Continuity mistake: In the scene where Monk meets Salvatore Lucarelli (Philip Baker Hall), Lucarelli is cutting up fisheads on a cutting board. Throughout the scene the fish on the table constantly change between shots. One of the notable changes is when Lucarelli is discussing the case he has for monk there is a shot of a fish, and when the shot changes you can now see the fish's head has all of a sudden been chopped off.
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