Mass. Gen. Laws ch. 43, § 96

The city council shall consist of seven or nine members, as provided in this section, all of whom shall, at each regular municipal election, be elected at large for terms of two years each by proportional representation as hereinafter provided and shall serve until their successors are qualified. The city council in any city having seven wards or less at the time of adoption of this plan shall be composed of seven members and the city council in any city having more than seven wards at the time of adoption thereof, nine members. Section eight of chapter thirty-nine shall apply to members of the city council. All trustees or other officers mentioned in section ninety-five shall at each regular municipal election be elected at large for terms of two years each by proportional representation as hereinafter provided.