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 Public Employees' Retirement Law, as it now exists or hereafter may be amended, to enable the City to continue as a contracting City under the Public Employees' Retirement System. The City Council may terminate the contract with the Board of Administration of the Public Employees' Retirement System, whereby all employees are members of the System, only under authority granted by ordinance adopted by majority vote at a City election.