Is it in your lease that you have to use the Labor Union for your TI's?? I cant believe that was not discussed with you prior to the lease. If it's not in your lease have your attorney tell them to piss off!
And also it's normal only related to "permanent" construction like the fire alarm, partition walls, ceilings etc. normally any temporary or "decorative" structures are completely exempt (including workstations or cubicles which our maze's are basically the same thing) . Can you imagine Nordstrom contracting through he mall's union every time they move the shoe stands or clothing hangers around when they change the store layout a little bit??
I am sure your attorney has looked into all this, but this crap pisses me off!
What?? You dropped your cell phone in the Haunted house somewhere and wanted to know if I could go get it for you? Sorry, that's against the rules but I will let you go to the front of the line so you can go try to find it yourself. Just give me a moment to let the monsters know you are coming through again...Alone.