Within sixty days after the enactment by the council of any ordinance authorizing the issuance of bonds, notes or other evidence of debt the repayment of which requires a pledge of the full faith and credit of the municipality, a petition signed by the qualified electors of the municipality equal in number to at least fifteen percent of the registered voters at the last preceding regular municipal election may be filed with the municipal clerk requesting that any such ordinance be repealed; provided, however, that this section shall not apply to bond issues approved by referendum or to notes issued in anticipation of taxes.