(a) Allowance.--If a city has entered into an agreement with the Commonwealth to place certain employees under the Social Security Act (49 Stat. 620, 42 U.S.C. § 301 et seq.), the board may authorize any joint coverage member of the retirement system to elect, according to the provisions of this section, to receive compensation without the reduction provided for in section 14343 (relating to retirement allowance, proof of disability and joint and single coverage members defined), provided that the member shall make a lump-sum payment to the board or installment payments, as may be approved by the board, equal to the difference between the amount of the accumulated fund to the member's credit in the fund as of the last date for which salary or wages was paid and the amount which would have been to the member's credit in the fund if contributions had been made on that portion of the member's salary or wages on which Social Security allowances are payable at the same rate as made on that portion of the member's salary or wages in excess of that on which Social Security allowances are payable, from the time that the salary or wages became subject to Social Security coverage. Election shall be made in writing, in the form prescribed by the board, and shall be accompanied by the lump-sum payment or an agreement as to installment payments.

(b) Election.--The board may authorize a member to make the election under subsection (a) at any time, and, if made prior to retirement, the member shall, in addition to any lump-sum or installment payments required, pay to the board contributions on the member's entire salary or wages received after the election at the rate provided in this subchapter for monthly salary or wages in excess of that on which Social Security allowances are payable.