N.J. Stat. § 43:10-18.75
Any employee who, on the effective date of this amendatory and supplementary act, is a member of this retirement system and whose then annual salary is more than $5,000.00, may receive credit for pension purposes for the total amount of his said annual salary, upon written application to the pension commission within 90 days from the said effective date of this amendatory and supplementary act, and upon payment into this retirement system a sum equal to the total amount which said employee would have theretofore paid for service or would have had deducted from his salary, had there been no maximum salary limitation for pension purposes in effect during the entire time of such employee's membership in this retirement system, less the amount already paid for service or the amount already deducted from his salary for pension purposes under the act to which this act is amendatory and supplementary. Such payment shall be made either by lump sum or by deductions from salary, at the election of the employee, in which event interest at the rate of 3% per annum shall be charged on the unpaid balances, but in no case shall such payments be spread over a period of more than 5 years.
N.J.S. § 43:10-18.75