N.J. Stat. § 40A:9-1.4
Any local unit having adopted the provisions of Title 11 (Civil Service) of the Revised Statutes, which has also adopted the provisions of section 1 of this act by ordinance or resolution, as appropriate, may therein limit the eligibility of applicants for positions and employments in the classified service of such local unit to residents of that local unit. Upon receipt of a copy of such ordinance or resolution, as the case may be, the Civil Service Commission thereafter shall not open such local unit's eligibility lists to anyone who is not a bona fide resident of the local unit at the time of the closing date following the announcement of examination; provided, however, that if the commission, after ample advertisement, determines that an insufficient number of qualified residents exist for available positions or employments in a particular local unit, it may open eligibility lists for such positions or employments to qualified nonresidents.
N.J.S. § 40A:9-1.4