Mass. Const. amend. art. VIII

No judge of any court of this commonwealth (except the court of sessions) and no person holding any office under the authority of the United States (postmasters excepted) shall, at the same time, hold the office of governor, lieutenant governor, or councillor, or have a seat in the senate or house of representatives of this commonwealth; and no judge of any court in this commonwealth (except the court of sessions) nor the attorney-general, solicitor-general, county attorney, clerk of any court, sheriff, treasurer and receiver-general, register of probate, nor register of deeds, shall continue to hold his said office after being elected a member of Congress of the United States, and accepting that trust; but the acceptance of such trust by any of the officers aforesaid shall be deemed and taken to be a resignation of his said office; and judges of the courts of common pleas shall hold no other office under the government of this commonwealth, the office of justice of the peace and militia offices excepted.