Sounds pretty much like "bully boy" tactic, a group of men getting a union rep to go and have a word with a new girl because she is doing the job she has been told to do.
If the blokes have a problem then by all means get the union involved but the rep should have talked to the management who assigned her the job, not gone and asked her sarcastic questions. Having him go up to her after probably being seen conferring with the group of blokes who are standing there watching could seen as quite intimidating.
What plant are you at? I was assuming Halewood as AFAIK employee parking at Castle Brom and Solihull is off site, but your user name (carlbcfc)confuses matters. Can't say my, or anyone I know at work, experience with management bares any resemblance to your slightly paranoid seeming accusations.
Oh, and what happened to the MSE thread?