Power of referendum; time for filing petition

The voters shall also have the power of referendum which is the power to approve or reject at the polls any ordinance submitted by the council to the voters or any ordinance passed by the council, against which a referendum petition has been filed as herein provided. No ordinance passed by the municipal council, except when otherwise required by general law or permitted by the provisions of section 17-32(b) of this act, shall take effect before twenty days from the time of its final passage and its approval by the mayor where such approval is required. If within twenty days after such final passage and approval of such ordinance a petition protesting against the passage of such ordinance shall be filed with the municipal clerk and if the petition shall be signed by a number of the legal voters of the municipality equal in number to at least 15% of the total votes cast in the municipality at the last election at which members of the General Assembly were elected, the ordinance shall be suspended from taking effect until proceedings are had as herein provided. The provisions of this section shall not apply to any ordinance which by its terms or by law cannot become effective in the municipality unless submitted to the voters, or which by its terms authorizes a referendum in the municipality concerning the subject matter thereof.