N.J. Admin. Code § 13:14-1.8
An employee on family leave may not engage in other full-time employment during the term of the leave, unless such employment commenced prior to the leave and is not otherwise prohibited by law. During the term of family leave an employee may commence part-time employment which shall not exceed half the regularly scheduled hours worked for the employer from whom the employee requested leave. An employee may continue part-time employment which commenced prior to the employee's family leave, at the same number of hours that the employee was regularly scheduled at that part-time employment prior to such leave. An employer may not maintain a policy or practice which prohibits part-time employment during the course of a leave or prohibits continuation of lawful full-time employment that commenced prior to the leave.
N.J. Admin. Code § 13:14-1.8