Section 42. If, within twenty days after the final passage of any measure, except a revenue loan order, by the city council or by the school committee, a petition signed by registered voters of the city, equal in number to at least twelve percent of the total number of registered voters, and addressed to the city council or to the school committee, as the case may be, protesting against such measure or any part thereof taking effect, is filed with the city clerk, the same shall thereupon and thereby be suspended from taking effect; and the city council or the school committee, as the case may be, shall immediately reconsider such measure or part thereof; and if such measure or part thereof is not entirely rescinded within twenty days after the date of the certificate of the registrars, the city clerk shall submit the same, by the method herein provided, to a vote of the registered voters of the city, either at the next regular city election not less than thirty days after said twentieth day, or at a special election which the city council may, in its discretion, call for the purpose, and such measure or part thereof shall forthwith become null and void unless a majority of the registered voters voting on the same at such election vote in favor thereof.

The petition described in this section shall be termed a referendum petition and section thirty-eight shall apply to the procedure in respect thereto, except that the words ''measure or part thereof protested against'' shall for this purpose be understood to replace ''measure'' in said section wherever it may occur, and ''referendum'' shall be understood to replace the word ''initiative'' in said section.