Mass. Gen. Laws ch. 51 § 15
Except as provided in section seventeen, there shall be in every city, other than one having a board of election commissioners or an election commission, and in every town a board of registrars of voters consisting of the city or town clerk and three other persons who shall, in a city, be appointed by the mayor, with the approval of the aldermen, and in a town, by a writing signed by the selectmen and filed with the town clerk. When a board of registrars is first appointed, the registrars shall be appointed in February or March for terms respectively of one, two and three years, beginning with April first following. In February or March in every year after the original appointment, one registrar shall be appointed for the term of three years, beginning with April first following.
As the terms of the several registrars expire, and in case a vacancy occurs in the board of registrars of voters, the selectmen or the appointing authority shall so appoint their successors that as nearly as possible the members of the board shall represent the two leading political parties, as defined in section one of chapter fifty; provided, that a city or town clerk need not be enrolled in a political party; and provided further, that in no case shall an appointment be made as to cause a board to have more than two members, including the city or town clerk, of the same political party. Every such appointment shall be made in a town by the selectmen or the appointing authority from a list to be submitted to them by the town committee of the political party from the members of which the position is to be filled, containing the names of three enrolled members of such party resident in the town, selected by a majority vote at a duly called meeting, at which a quorum is present, of such committee; and every member of a board of registrars of voters shall serve until the expiration of his term and until his successor has qualified; provided, however, if the chairman of the town committee has not submitted such list to the selectmen or the appointing authority within forty-five days after a notification to said chairman by certified mail, the selectmen or the appointing authority shall make said appointment without reference to such a list.
Mass. Gen. Laws ch. 51, § 15