Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 54, § 141

Upon a vacancy in the office of representative in the general court or upon failure to elect, the speaker of the house of representatives shall issue precepts to the aldermen of each city and the selectmen of each town comprising the district or any part thereof, appointing such time as the house of representatives may order for an election to fill such vacancy; provided, that if such vacancy occurs during a recess between the first and second annual sessions of the same general court, the speaker may fix the time for an election to fill such vacancy. All such elections shall be held on a Tuesday. Upon receipt of such precepts, the aldermen or the selectmen shall call an election, which shall be held in accordance with the precepts.