N.J. Stat. Ann. § 43:21-36

Nothing in this act shall be construed to prohibit the establishment by an employer, without approval, of a supplementary plan or plans providing for the payment to employees, or to any class or classes thereof, of benefits in addition to the benefits of an approved private plan, or to prohibit the collection or receipt of additional voluntary contributions from employees toward the cost of such additional benefits. The rights, duties and responsibilities of all interested parties under such supplementary plans shall be unaffected by any provision of this act.