N.J. Stat. Ann. § 43:16A-3.5

1. Any member of the Police and Firemen's Retirement System of New Jersey who has been or shall be elected to the position of sheriff or who has accepted or shall accept appointment to the office or position of undersheriff may, by written notification to the board of trustees and the county treasurer, elect to continue to be a member of the retirement system while serving as sheriff or undersheriff and shall be deemed to have waived any and all benefits to which he would otherwise be entitled by eligibility for membership in the Public Employees' Retirement System. The county treasurer shall make deductions from the salary of the sheriff or undersheriff and contributions on his behalf to the Police and Firemen's Retirement System as is required by law for members of that system.