Section 6A. Notwithstanding the provisions of any city charter to the contrary, the mayor and the members of the city council, or other legislative body of a city, shall receive for their services such salary as the city council or other legislative body of a city shall by ordinance determine, and shall receive no other compensation from such city, except that a member of a city council of said city may receive a salary for serving as an instructor in a municipal college of such city, except that a member of a city or town council in a municipality with a city or town council form of government may receive a salary for serving as a municipal employee of said municipality in lieu of receiving compensation for serving as a member of said council and except that, in accordance with the provision of the seventh paragraph of section twenty of chapter two hundred and sixty-eight A, any elected municipal official, other than a mayor, may choose to receive either the compensation for such service or compensation for service as an employee of a housing authority in such municipality, but may not receive both. No increase or reduction in such salaries shall take effect during the year in which such increase or reduction is voted, and no change in such ordinance shall be made between the election of a new council or other legislative body and the qualification of the new council or other legislative body. Such ordinance shall be subject to the provisions of sections forty-two, forty-three and forty-four of chapter forty-three.