Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 48, § 57D

If any permanent member of the fire fighting force or fire alarm division of a fire department of a city or town which accepts this section is required to be on duty at any time on 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 in the case of any such member whose regular day off or vacation day or a day on which he is absent from duty because of injuries received in the performance of his duties falls on any of the aforementioned holidays, an additional day off shall be allowed, or payments in lieu of one day shall be allowed. Such day's pay shall be one fifth of his regular weekly salary.Section fifty-seven A shall not apply in any such city or town.