The electors shall have a power to approve or reject at the polls any ordinance passed by the Council, or submitted by the Council to a vote of the electors, except an appropriation ordinance, such power being known as the referendum. Ordinances submitted to the Council by initiative petition and passed by the Council without change, or passed in an amended form and not required by the committee of the petitioners to be submitted to a vote of the electors, shall be subject to the referendum in the same manner as other ordinances.