Mass. Gen. Laws ch. 32B § 9E
A county, except Worcester county, by vote of the county commissioners; a city having a Plan D or Plan E charter by majority vote of its city council; in any other city by vote of its city council, approved by the mayor; a district, except as hereinafter provided, by vote of the registered voters of the district at a district meeting; a regional school district by vote of the regional district school committee; a veterans' services district by vote of the district board; a welfare district by vote of the district welfare committee; a health district established under section twenty-seven A of chapter one hundred and eleven by vote of the joint committee may provide that it will pay in addition to fifty per cent of a stated monthly premium as described in section seven A for contracts of insurance authorized by sections three and eleven C, a subsidiary or additional rate which may be lower or higher than the aforesaid premium and the remaining fifty per cent of said premium is to be paid by a retired employee under the provisions of the first sentence of section nine. A town shall provide for such payment by vote of the town or if a majority of the votes cast in answer to the following question which shall be printed on the official ballot to be used at an election in said town is in the affirmative: "Shall the town, in addition to the payment of fifty per cent of a premium for contributory group life, hospital, surgical, medical, dental and other health insurance for employees retired from the service of the town, and their dependents, pay a subsidiary or additional rate?" Section nine A shall not apply in any governmental unit which accepts the provisions of this section. No governmental unit, however, shall provide different subsidiary or additional rates to any group or class within that unit.
Mass. Gen. Laws ch. 32B, § 9E