If the petition accompanying the proposed ordinance is signed by registered voters of the city of Hamtramck equal in number to at least ten percent (10%) but less than twenty percent (20%) of the vote cast for all candidates for mayor of the city at the last preceding general municipal election at which a mayor was elected, which number shall be not less than two hundred and fifty (250), as shown in the manner hereinafter provided, and the ordinance be not passed without alteration by the council within twenty (20) days as provided in the preceding section, then the ordinance, without alteration, shall be submitted by the council to electoral vote at the next regular election that shall occur at any time after thirty (30) days from the date of the city clerk’s certificate of sufficiency attached to the petition accompanying the ordinance.