Overly broad discovery requests are fun but there's a good response - imagine getting 500,000 pages of text from the company's records department, in shuffled order, with hand written notes, and copies of faxed printouts of email so illegible OCR gives up. Oh, and the incriminating stuff is accidentally missing (or did you just not find it yet?)
That's assuming the discovery request isn't ignored or thrown out by the court. Also, their lawyers are better than yours, and they're in-house (not hourly) and really bored. Your only recourse ends up being bad PR, but that makes finding a new job harder, so it's lose-lose.
But if you have a union....