Is It a case of, not registered then no Pesel, no pesel then not able to work legally.
If that is the case, it's a new law and one that I have never heard of. I personally do not have a PESEL and have never had one. However, I think that PESEL numbers are generated at the same place as where you get your maldunek. Personally I have a NIP number and whenever people want a PESEL number I just tell them to either use my passport number or my NIP number or make up a number or simply not do business with me (nobody has ever chosen the last option).