N.J. Stat. Ann. § 43:16A-3.9

2. A policeman or fireman employed after the effective date of this supplementary act by a municipality, which was not required to participate in PFRS under section 3 of P.L.1944, c.255 (C.43:16A-3) and has not adopted that act, and a fireman employed after the effective date of this supplementary act by a fire district in which the provisions of P.L.1944, c.255 are not operative on that effective date, who meets the requirements for membership in the PFRS shall be required to enroll in the retirement system as a condition of employment.