The city commission shall at once proceed to consider such petition and shall take final action thereon within thirty (30) days from the date of submission. If the city commission rejects the proposed ordinance, or passes it in a different form from that set forth in the petition, or fails to act finally upon it within the time stated, the committee of the petitioners by written demand filed with clerk of the city commission not later than twenty (20) days after final action or inaction by the city commission, may require that the proposed ordinance be submitted to a vote of the electors in its original form, if, with or prior to such demand, a petition for such election, signed after the final action for inaction of the city commission is filed with such clerk bearing additional signatures of five percent (5%) of the registered voters of the city at the last election, none of whom were signers of the first petition. Such clerk shall forthwith cause notice of the filing of such demand and petition to be published in some newspaper of general circulation in the City, and shall also within five (5) days certify to the officers having control of elections the proposed ordinances, stating whether or not a special election is demanded in the petitions, the percentage of registered voters at the last municipal election who signed the two petitions in the aggregate, and the date on which he published the notice last mentioned.