Mass. Gen. Laws ch. 48 § 57A
If any permanent member of the fire fighting force or fire alarm division of a fire department of a city or town is required to serve a tour of duty during the twenty-four hour period commencing at eight o'clock in the morning of January the first, July the fourth or Christmas day, or the day following when any of said days occurs on Sunday, or the third Monday in February, the third Monday in April, the last Monday in May, the first Monday in September, the second or fourth Monday in October or Thanksgiving day, he shall be given an additional day off, or, if such additional day off cannot be given because of personnel shortage or other cause, he shall be entitled to an additional day's pay; provided, that any such member who, through a rotation of shifts, works different days in successive weeks shall be granted, in each year in which the number of holidays falling on his regular days off is in excess of the number of holidays in such year falling on Saturday, additional days off equal to the excess, and, if any such additional day off cannot be given because of personnel shortage or other cause, an additional day's pay shall be allowed in lieu thereof. This section shall take effect in a city having a Plan E charter when accepted by the affirmative vote of a majority of the city council, and in the case of other cities by vote of the city council, subject to the provisions of its charter, and in a town by a majority vote at an annual town meeting, but not otherwise.
Mass. Gen. Laws ch. 48, § 57A