Section 10. (a) Amendments to a city or town charter previously adopted or revised under this chapter may be proposed by the city council of a city or the town meeting of a town by a two thirds vote in the manner provided by this section; provided, that amendments of a city charter may be proposed only with the concurrence of the mayor in every city that has a mayor, and that only a charter commission elected under this chapter may propose any change in a charter relating in any way to the composition, mode of election or appointment, or terms of office of the legislative body, the mayor or city manager, or the board of selectmen or town manager. In this section, the word ''mayor'' shall mean an officer elected by the voters as the chief executive officer of a city or an officer lawfully acting as such, and the term ''two thirds vote'' shall mean, in cities, a vote, taken by yeas and nays, of two thirds of the members of a city council present and voting thereon, and shall mean, in towns, the vote of two thirds of the voters present and voting at a duly called meeting.

(b) In addition to any amendment proposed by a city council or town meeting under subsection (a) the city council or town meeting shall consider and vote upon any suggested charter amendment which it would have the power to propose under subsection (a), and which is not substantially the same as an amendment already considered and voted upon by it within the last twelve months, and which is suggested to it in a written request signed by the mayor or city manager or any member of the city council in a city or by the town manager or any selectman of a town, or is suggested to it by a petition in substantially the form set forth in section fifteen, signed and completed in accordance with the instructions contained therein by at least ten registered voters in the case of a town and by as many registered voters, in the case of a city, as would be required to nominate a charter commission member in such city under section five, which written request or petition shall be filed with the city or town clerk.

At the earliest convenient time not later than three months after the date any suggested amendment is filed with the city or town clerk, the city council or board of selectmen shall order a public hearing to be held thereon before it or before a committee selected or established by it for the purpose, provided that any number of suggested amendments may be considered at the same hearing. Such a hearing shall be held not later than four months after the filing date of any suggested amendment to be considered, and at least seven days notice of such public hearing shall be published in a newspaper of general circulation in the city or town. Except where the hearing is held by a city council, the board or committee holding the public hearing shall report its recommendations to the city council or town meeting, as the case may be. Final action on such a suggested amendment shall be taken not later than six months after such filing date in the case of a city and, in the case of a town, not later than the first annual town meeting held at least six months after such filing date, provided that at any time after the public hearing two hundred registered voters of a town or twenty per cent of the total number of registered voters of such town, whichever is less, may in writing request the selectmen to call a special town meeting to consider the suggested amendment, and the selectmen shall thereupon call such meeting which shall be held not more than forty-five days after the receipt of the request.

(c) Whenever an order proposing a charter amendment to the voters is approved by the mayor and city council or town meeting, a copy of the proposed amendment shall be immediately submitted to the attorney general and to the department of housing and community development and such order shall not take effect for four weeks after the date of such submission. Within such four weeks the attorney general shall furnish the city council or board of selectmen with a written opinion setting forth any conflict between the proposed amendment and the constitution and laws of the commonwealth. A copy of the opinion shall at the time be furnished to the department of housing and community development. If the attorney general reports that the proposed amendment conflicts with the constitution of laws of the commonwealth, the order proposing such amendment shall not take effect except as may be specified by further proceedings of the mayor and city council or town meeting under subsection (a). If the attorney general reports no such conflict, such order shall become effective four weeks after its submission to the attorney general.

(d) No order or vote under subsection (a), (b) or (c) shall be subject to referendum or shall, except as provided in subsection (a), require the concurrence of the mayor.

(e) The provisions of subsections (a), (b), (c) and (d) shall apply to amendments of laws having the force of a city or town charter by virtue of section nine of Article LXXXIX of the Amendments to the Constitution as well as to amendments of a charter previously adopted or revised under this chapter.