§ 551. Optional retirement of certain members. a. Any member may elect to contribute to the retirement system on the basis of retirement upon his or her completion of twenty-five years of total creditable service on an allowance of one-fiftieth of his or her final average salary for each year of total service as a member but not exceeding in the aggregate one-half of his or her final average salary. Any member of the retirement system may elect to become a member pursuant to the provisions of this section within one year after he or she becomes a member, if his or her employer has elected to make the benefits provided herein available to members, or within one year after his or her employer elects to make the benefits provided herein available to its members.

b. Elections made pursuant to this section shall be in writing and shall be duly acknowledged and filed with the comptroller. Any member who files such an election pursuant to this section may withdraw it after it has been filed for at least one year. Such withdrawal shall be by written notice duly acknowledged and filed with the comptroller.

c. The member's employer by appropriate action shall, in its initial action under this section, elect to assume all of the additional cost on account of service as a member rendered prior to the effective date of such election and in any subsequent action, shall elect to assume all of the additional cost on account of service as a member of any such other prior department or force rendered prior to the effective date of such subsequent election. The employer shall pay the additional cost so assumed by any such election by means of annual contributions which shall be determined by the actuary of the retirement system and paid by the employer in the same manner as the contributions required under this chapter.

d. For actuarial purposes relative to rates or amounts of contributions to the funds of the retirement system, service of a member making an election pursuant to this section shall, as to his or her service and status subsequent thereto, be deemed continuous and constant. If the continuity of such service be interrupted or such status be changed, however, appropriate changes as may be necessary for actuarial purposes shall be made in such rates and amounts.

e. In the event a member shall continue in service after twenty-five years of total creditable service, there shall be added to his or her pension upon retirement a sum equal to one-sixtieth of his or her final average salary for each completed additional year of service after twenty-five years; provided, however, that upon completion of twenty-five years of total creditable service, a participating employer may elect to provide any service credit earned with a public employer prior to services performed as a sheriff, undersheriff or deputy sheriff towards the one-sixtieth allowance and provided, further that the total allowance payable pursuant to this section shall not exceed three-quarters of such member's final average salary.

f. The increased pension provided for in subdivision e hereof shall be conditioned upon the participating employer electing to provide this added benefit and assuming the additional cost thereof on account of all of the members. Such increased pensions to the members shall be paid from additional contributions made by the appropriate participating employer on account of such members. The actuary of the retirement system shall compute the additional contributions for each employer who elects to provide the special benefits so provided. Such additional contributions shall be computed on the basis of contributions during the prospective service of such members which will cover the liability of the retirement system for such extra pensions. Upon approval of the comptroller, such additional contributions shall be certified by him to the chief fiscal officer of the participating employer. The amount thereof shall be included in the annual appropriation of the participating employer for members. Such amount shall be paid on the warrant of the chief fiscal officer of the participating employer to the pension accumulation fund of the retirement system.

g. Any member may, within one year after he or she becomes a member or within one year after his or her employer assumes the additional cost therefor, whichever shall last occur, elect to receive the additional benefits provided for by subdivision e hereof. Any member who elects to receive such benefits shall be separated from service on the first day of the calendar month next succeeding his or her attainment of age sixty-two and the completion of twenty-five years of service, provided, however, that in the case of any member who attained the age of sixty-two before his or her employer assumed the additional cost therefor, or who attains the age of sixty-two within one month after his or her employer assumes the additional cost therefor, to be eligible for additional pension credit under subdivision e of this section, his or her service shall be terminated and he or she shall be retired within three months after his or her employer assumes the additional cost therefor.

h. 1. As used in this section "creditable service" shall include, any and all services performed as a sheriff, undersheriff or deputy sheriff, provided, however, that criminal law enforcement service shall only be creditable when it aggregates fifty per centum or more of his or her service as a deputy sheriff. Credit for service as a member or officer of the state police or as a paid firefighter, police officer or officer of any organized fire department or police force or department of any county, city, village, town, fire district or police district, or as a criminal investigator in the office of a district attorney, provided that service as such investigator shall have been rendered prior to January first, nineteen hundred sixty and that credit therefor shall not exceed five years, shall also be deemed to be creditable service and shall be included in computing years of total service for retirement pursuant to this section, provided such service was performed by the member while contributing to the retirement system pursuant to the provisions of this article or article eight of this chapter.

2. Notwithstanding the provisions of paragraph one of this subdivision, a participating employer may elect on a form filed with the comptroller for that purpose to provide that creditable service shall also include any and all service performed by a deputy sheriff who is a police officer pursuant to subdivision thirty-four of section 1.20 of the criminal procedure law as certified by the municipal police council or as certified by the police department of the city of New York upon satisfactory completion of the basic training program and graduation from the New York city police academy.

i. In computing the twenty-five years of completed service of a member, full credit shall be given for military service as defined in subdivisions twenty-nine-a and thirty of section three hundred two of this chapter.

j. The provisions of this section shall be controlling notwithstanding any provision of this chapter to the contrary.

k. The benefits hereinabove provided shall be payable to a member, unless at the date of retirement, such member would otherwise be entitled to a greater benefit under other provisions of this chapter had he or she withdrawn from this section, in which event such greater benefits shall be payable.