53 Pa. Stat. § 13301
Hereafter, no political subdivision of this Commonwealth, nor any part thereof, shall be annexed to any city of the first class in accordance with the provisions of any existing law providing for such annexation, unless the voters of the entire political subdivision have first consented to such annexation. Whenever any proceeding for such annexation shall be commenced, the same shall not be concluded and the annexation shall not become effective until there has first been submitted to the electors of the entire political subdivision, in accordance with the election law for the submission of such questions, a proper question to ascertain the will of the electors with respect to such proposed annexation. Such question shall be printed on ballots provided by the county commissioners, and shall be submitted at any general or municipal election occurring at least sixty days after a petition shall have been filed with the county commissioners by the council of the city of the first class to which such annexation is to be made, asking for the submission of such question. If, at any such election, a majority of those voting on such question shall consent to such annexation, then such annexation may be made and concluded in the manner provided by law, but if a majority of those voting on the question shall vote against such annexation, then no further proceedings for such annexation shall be had. Any such question shall not be submitted oftener than once in five years. Nothing contained in this act shall be construed to apply to proceedings under existing law where provision is now or hereafter made to secure the consent of the electors of any political subdivision to any such annexation.
53 P.S. § 13301