950 CMR, § 47.16
All ballots transmitted under any provision of 950 CMR 47.00 shall be subject to challenge. Any challenge must be made when the affidavit envelope containing the early voting ballot is opened and the ballot is deposited into the ballot box for non-compliance with any provision of 950 CMR 47.08, 47.09(5), 47.10(5) or for any other reason allowed by law. If an early voting ballot is challenged, it shall be processed in accordance with 950 CMR 52.03(23): Challenges and 54.04(23): Challenges, except that so much of said section as involves the administering of an oath shall not apply thereto, and the writing of the name and address of the voter on the ballot shall be performed by the officer charged with depositing the ballot in the ballot box.
950 CMR, § 47.16