Probably never or very rarely fraud. If you work "at-will" there's explicitly no restriction against working multiple jobs unless its specified by an employmen

Probably never or very rarely fraud. If you work "at-will" there's explicitly no restriction against working multiple jobs unless its specified by an employment contract (which few people in "at-will" employment regions have). Of course, each employer may have a policy forbidding it and thus could fire you on at-will terms if they found out, but that's a long way away from fraud in any legal sense. Fraud is a lot more specific than just lying (either outright or as would be the case most often when it comes to having multiple jobs: lying by omission). I'm not defending the act of working multiple jobs with full-time expectations here, I think in many cases it would be at best unprofessional, but it would take a very specific set of circumstances for it to come close to reaching the high bar of fraud.