Any undertaking or promise such as is described in this section, or any other undertaking or promise in conflict with the public policy declared in section two of this act, is hereby declared to be contrary to the public policy of this Commonwealth, shall not be enforceable in any court of this Commonwealth, and shall not afford any basis for the granting of legal or equitable relief by any such court against a party to such undertaking or promise, or against any other persons who may advise, urge or induce either party thereto to act in disregard of such undertaking or promise, including specifically the following:

Every undertaking or promise hereafter made, whether written or oral, express or implied, constituting or contained in any contract or agreement of hiring or employment between any individual, firm, company, association or corporation, and any employe or prospective employe of the same whereby--