Except for any period of current service in which the making of regular member contributions has ceased solely by reason of section 5502.1 (relating to waiver of regular member contributions and Social Security integration member contributions) or any provision of this part relating to limitations under IRC § 401(a)(17) or 415, contributions shall be made on behalf of an active member of any class who prior to March 1, 1974, has elected Social Security integration coverage. The amount of such contributions shall be 6 ¼ % of that portion of his compensation as an active member in excess of the maximum wages taxable under the provisions of the Social Security Act (49 Stat. 620, 42 U.S.C. § 301 et seq.), in addition to the regular member contributions which, after such election, shall be determined on the basis of the basic contribution rate of 5% and the additional member contribution of 1 ¼ %: Provided, That a member may elect to discontinue Social Security integration coverage and shall thereafter be ineligible to accrue any further Social Security integration credits or any additional benefits on account of Social Security integration membership.