Mass. Gen. Laws ch. 54 § 23
Upon the written petition of ten qualified voters of a ward or of a town, presented at least twenty-one days before a state or city election therein, the governor may appoint, for such ward or town for each voting precinct named in the petition, two voters of the city or town, who shall not be signers of the petition or members of any political committee or candidates for any office, to act as supervisors at such election. One supervisor shall be appointed from each of the two leading political parties. They shall be sworn by the city or town clerk or by an officer qualified to administer oaths. The supervisors shall attend the polling places for which they are appointed, may challenge persons offering to vote, and shall witness the conduct of the election and the counting of votes; but they shall not make any statement tending to reveal the state of the polls before the public declaration of the vote. They shall remain where the ballot boxes are kept after the polls are open and until the ballots are sealed for transmission to the officers entitled to receive them. Each supervisor may affix his signature, for the purpose of identification, to the copy of the record of votes cast, or attach thereto any statement touching the truth or fairness or conduct of the election. Supervisors shall receive such compensation as the city council or selectmen may determine.
Any supervisor appointed under this section violating any provision of this section, or any person who prevents any such supervisor from doing any of the acts authorized by this section, or hinders or molests him in doing any such acts, or aids or abets in preventing, hindering or molesting him in doing any of such acts, shall be punished by a fine of not more than five hundred dollars or by imprisonment for not more than six months.
Mass. Gen. Laws ch. 54, § 23