If at any time within twenty (20) days after passage of an ordinance which was not passed by at least a two-thirds (2/3) majority of members elected to Council, a petition signed by electors equal in number to at least ten percent (10%) of the total vote cast at the last preceding regular municipal election of the City is filed with the Clerk of the Council requesting that any such ordinance, or any specified part thereof, be repealed or submitted to a vote of the electors, it shall not become operative with respect to any actions or obligations not yet undertaken under the ordinance, until the steps indicated herein have been taken. The petition shall be prepared and filed in the manner and form prescribed in the foregoing sections of this Charter for an initiative petition for an ordinance. An ordinance passed by at least a two-thirds (2/3) majority of members elected to Council shall not be subject to referendum. (Amended 11-7-44; 5-7-13)