Is it illegal for my employer not to pay overtime?

If you are a non-exempt employee, yes – the FLSA requires 1.5x your regular rate for hours over 40 in a workweek, and PA and NJ enforce overtime as well. Failing to pay it, misclassifying you as exempt, or not counting all hours worked (including off-the-clock time) can entitle you to back pay and, in some cases, additional damages.