The voters 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 voters, except an appropriation ordinance or an ordinance making the annual tax levy, such power being known as the referendum. Ordinances 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 voters, shall be subject to the referendum in the same manner as other ordinances.