Section 8A. In any city which accepts this section upon its submission in accordance with law at its first regular city election following the effective date of this section, an order authorizing the issue of bonds, notes or certificates of indebtedness for any purpose specified in any applicable clause of section seven, other than clause (11), or for any purposes specified in section eight, other than clause (1), (2) or (9), shall not become effective before the expiration of a period of twenty days from the day upon which such order would become effective except for this section. If within said period a petition signed by registered voters of the city to the number of twelve thousand or equal in number to at least twelve per cent of the total number of such registered voters, whichever is the lesser, and conforming to the provisions of section thirty-eight of chapter forty-three relative to initiative petitions in cities governed by said chapter, shall be filed with the city clerk, such filing in cities subject to said section thirty-eight to be in the manner therein provided, asking that the question of approving or disapproving such order be submitted to the registered voters of the city, such order shall be further suspended from becoming effective and said city clerk shall forthwith transmit such petition to the city council, which shall immediately reconsider such order. If such order is not rescinded, the city council shall submit the same to a vote of the registered voters of the city, either at the next regular city election, or at a special city election which may, in the discretion of the city council, be called for the purpose in the manner provided by law. If an order submitted as aforesaid be approved by a majority of the registered voters voting on the question, such order shall at once become effective; but if not so approved such order shall have no effect. If a petition relative to any such order is not filed within said period of twenty days, such order shall become effective upon the expiration of said period.