Plenary authority and power are hereby vested in the City, its City Council and its several Officers, agents and employees to do and perform any act, or exercise any authority granted, permitted, or required under the provisions of the State Employees’ Retirement Act, as it now exists or may hereafter be replaced or amended, to enable said City to continue as a contracting city participating in the said retirement system. The City Council may terminate any such contract with the Board of Administration of the State Employees’ Retirement System only under authority granted by ordinance adopted by a majority vote of the electors of the City, voting on such proposition at any election at which such proposal is presented.