N.J. Stat. § 40:54-29.4
The governing bodies of such municipalities shall propose such an undertaking by a joint library agreement, which shall provide for the apportionment of annual and special appropriations therefor among such municipalities, for the initial annual appropriation for such library, for the abandonment or the continuance of such agreement in the event that it is not approved by all such municipalities as provided for in this act, and for such other matters as they shall determine. Such apportionment of appropriations may be based on the assessed valuations of the respective municipalities, their populations, or such factor or factors as the governing bodies shall agree.
Such an agreement shall provide that the combined minimum appropriation for the joint library shall annually be not less than one-third of a mill on every dollar of assessable property within the participating municipalities based upon the equalized valuation of such property within the combined municipalities as certified by the Director of the Division of Taxation in the Department of the Treasury.
N.J.S. § 40:54-29.4