The effective date of coverage of members under the Social Security provisions, by a modification of the federal-state old-age and survivors disability insurance agreement shall be made retroactive to the earliest date permissible under such provisions. Contributions required of each member under such provisions for time prior to the federal execution date of such modification, shall be paid from such member's accumulated contributions held by the system on account of his or her compensation not in excess of the maximum compensation taxable under such provisions for such retroactive time. If the required contributions under such provisions exceed the member's accumulated contributions held by the system so determined, contributions under such provisions equal to the excess shall be paid by the member. Contributions required under such provisions of the employer on account of time prior to such execution date shall be paid from funds held by the system on account of active members and derived from contributions of the city. (Prior code § 34.10.1004)