N.J. Stat. § 43:15A-39.1
Any member who serves, while on an approved leave of absence from regular duties, as an officer or representative of a local, county or State labor organization which represents, or is affiliated with an organization which represents, public employees shall have the option to receive credit in the retirement system for the service. Any member who chooses to receive the credit shall be liable, with respect to the service to be credited, for payment to the retirement system of both the contributions that would have been required under section 25 of P.L. 1954, c.84 (C.43:15A-25) and section 30 of P.L. 1954, c.84 (C.43:15A-30) and the contributions that would have been required under section 24 of P.L. 1954, c.84 (C.43:15A-24) if that service had been rendered as regular service to the employer granting the leave of absence. The contributions shall be based upon the compensation that would have been received by the member under the negotiated salary guide of the employer granting the leave had that member remained in service with that employer, including applicable normal increments and negotiated wage increases occurring during the period of the leave.
N.J.S. § 43:15A-39.1