Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 40, § 5A

To provide for extraordinary or unforeseen expenditures, a city may, prior to the date when the tax rate for a fiscal year is fixed, include in the appropriations for such fiscal year as a reserve fund a sum not exceeding 5 per cent of the tax levy for the fiscal year next preceding such fiscal year. No direct drafts against this fund shall be made, but transfers from the fund may from time to time be voted by the city council upon recommendation of the mayor, and the city auditor or officer having similar duties shall make such transfers as are so voted.