The Council shall at once proceed to consider such petition and shall take final action thereon within thirty days from the date of submission. If the Council 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 the Clerk of the Council not later than twenty days after final action or in action by the Council, 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 or inaction of the Council is filed with such Clerk bearing additional signature of five percent of the electors of the city, 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 days certify to the officers having control of elections the proposed ordinance, stating whether or not a special election is demanded in the petitions, the percentage of voters who voted at the last election of municipal officers who signed the two petitions in the aggregate, and the date on which he published the notice last mentioned.