N.J. Stat. § 43:10-18.12
Once each year the pension commission may, and upon his application, shall, require any member retired for disability who is under the age of 60 years to undergo medical examination by a physician or physicians designated by the commission. The examination shall be made at the residence of the beneficiary or any other place mutually agreed upon. If the physician or physicians thereupon report and certify to the commission that the disability beneficiary is not permanently and totally incapacitated either physically or mentally for the performance of duty and that he is engaged in a gainful occupation, and if the commission concurs in the report, then the amount of his pension shall be reduced to an amount which, when added to the amount then being earned by him, shall not exceed the amount of the compensation now attributable to his former position. If subsequent medical examination of such a beneficiary shows that his earnings have changed since the date of his last examination, then the amount of his pension may be further altered but the new pension shall not exceed the amount of the pension originally granted nor shall the new pension when added to the amount then being earned by the beneficiary exceed the salary or compensation then attributable to his former position.
N.J.S. § 43:10-18.12