If you want to check your own employees, that's your business. The law needs to stay out of it, though.
The government already knows what I do or don't have to hide. If I'm to dangerous to work at a fair, I need to be in prison. If I have the right to be hired by a carnival, then the 14th amendment guarantees that every other US citizen has that right, too.
Every crowd has a silver lining - PT Barnum