The electors shall have power to approve or reject at the polls any ordinance passed by the commission, or submitted by the commission to a vote of the electors, except an appropriation ordinance, such power being known as referendum ordinance submitted to the commission by initiative petition and passed by the commission 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.