N.J. Stat. Ann. § 40:48B-20

The joint agreement may be terminated upon the adoption of a resolution to that effect by the governing body of either of the municipalities in the case of a joint assessing office comprising 2 municipalities, or 2/3 of the governing bodies in the case of a joint assessing office comprising 3 or more municipalities. Except by unanimous agreement, such termination shall not be made effective earlier than June 30 next succeeding the expiration of 12 full calendar months following the adoption of such resolution by the last of the required number of municipalities.