N.J. Stat. § 43:15A-16
The retirement system shall classify the members in such groups by age as it may determine for actuarial purposes.
The system shall further classify the membership by benefit rates as Class A or Class B members, as follows:
"Class A" shall include those members whose annuity shall be based on a per centum of salary, computed to be sufficient, with regular interest, to procure for the member, on retirement for service, an annuity equal to 1/140 of his final compensation for each year of service as a member.
"Class B" shall include those members who have elected or who shall hereafter elect to contribute to the annuity savings fund at a higher rate per centum, computed to be sufficient, with regular interest, to procure for the member, on retirement for service, an annuity equal to 1/120 of his final compensation for each year of service as a member.
Any new member after the effective date of this section shall be placed in "Class B."
N.J.S. § 43:15A-16