Part of a compromise on immigration has always been E-Verify, the process of bouncing a new employee's data against database(s) to confirm she is legal to work (i.e., has a green card). Conservatives push it, liberals tend not to be enthusiastic. (That's sort of weird, because conservatives generally resist government ID programs as an invasion of individual rights and liberals generally believe in government programs--but that's the way the human consistency cookie crumbles.)
So it's interesting when Cato comes out with a piece on the problems the program has in those states which have made it mandatory. Cato is libertarian enough that their results deserve a bit of salt, but the study shows relatively low compliance rates and a significant rate of false positives.
My uninformed analysis would suggest that a mandatory program by the feds could be much more effective, but others might disagree.