OP - as you can tell, we've had lively discussion on this thread. Where I disagree with some of the other posters is in the interpretation of FLSA in regards to exempt position.
My take is that if you are "exempt", they do NOT have to pay you overtime. I can agree with the other poster with that. in FLSA, they MUST pay you for working, not just for being 'billable'. Read thru the posts and then seek an employment attorney.
Thanks for the info Ginny J, and to everyone else who weighed in.
I saw many of the same FLSA and WI DWD excerpts when I was digging around on my own last year. But nothing seemed to address billable time vs. non-billable time -- hence, the "twist" in my thread title.
I guess I gave up the ghost when I came to the conclusion that even if vacation time is considered compensation and I was losing vacation time, they weren't paying me any less money, so I wasn't losing compensation - it was just coming from a different bucket.
Still, not having found anything that specifically addressed billable vs. non-billable time, the issue was still gnawing at me and I figured I'd take a shot in this forum.
Again, thank you all for weighing in.