Mass. Gen. Laws ch. 59 § 21D
The commissioner of revenue shall calculate the total limit applicable pursuant to sections twenty A and twenty-one C and section thirty-four of chapter seventy-one; provided, however, that he may adjust any such limit upon written application and pursuant to written guidelines issued by him in order to counterbalance the effects of extraordinary, non-recurring events which occurred during the base year, which were not within the purview of normal municipal financial practices, and would otherwise cause a limit to be set which would be inconsistent with that intended by said sections; and provided, further, that any such adjustment shall be explained in detail and in writing.
For the purposes of this section, the ordinary use of free cash to reduce the gross amount of revenue to be raised shall be considered as within the purview of normal municipal practices. The commissioner may require the presentation of such books, records or other information by any official of the commonwealth or any official of a city, town, district, county, governing body or regional governmental unit as he deems necessary. He shall certify the amount of each limit to the proper governing body or local appropriating authority. If any such limit is increased or decreased in accordance with the provisions of this section, the commissioner shall redetermine the limit accordingly and shall forthwith certify such increased or decreased limit to the proper governing body or local appropriating authority.
No tax rate shall be fixed in any city or town until such rate has been approved by the commissioner of revenue, and the commissioner shall not approve a rate for any city or town which fails to report any increase in assessed valuation as described in paragraph (f) of section twenty-one C or which would allow the amount of property taxes levied to exceed the limit or adjusted limit determined by said commissioner.
Mass. Gen. Laws ch. 59, § 21D