I encountered an exception. It was a government contractor that billed the government to do various tasks. Federal contracting law includes requirements for overtime pay.

I think the worst legal behavior would be to demand 7 hours and 59 minutes of unpaid overtime per week. Past that, federal law steps in. So at worst you'd be working a tiny bit less than 48 hours per week... or you'd get paid more, which is a solid disincentive for the company.