Mass. Gen. Laws ch. 51, § 18: Political representation by board of registrars

Section 18. In the original and in each succeeding appointment and in filling vacancies, registrars of voters shall be so appointed that the members of the board shall represent the two leading political parties, and in no case shall an appointment be so made as to cause a board to have more than two members, including the city or town clerk, of the same political party.