Mr. Monk and the Red Herring - S3-E10
Revealing mistake: When Julie's teacher is searching the name 'Larry Tilburn', he isn't typing into a search engine, virtual encyclopedia, or anything of the type, the computer just shows a blue screen with a popup message in the middle.
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