Mass. Gen. Laws ch. 40B § 10
Upon the designation of the regional planning and economic development district by the secretary of economic development, all cities and towns within the boundaries of the district shall become members of the district. The secretary of economic development may from time to time review the boundaries of the district so established and, if he deems it in the best interest of the district, he may with approval of a majority of the members of the regional planning and economic development commission include additional cities and towns, or he may exclude cities and towns from said district; provided, however, that prior to such increase or decrease in the membership of the district, the secretary of economic development shall consult with the mayor of a city, or the city manager in a city having a Plan D or Plan E form of government, or the selectmen of a town to be included or excluded from such district.
The city or town may, after it has been a member of a regional planning and economic development district for a period of not less than five consecutive calendar years, terminate its membership in the district by a two thirds vote of the city council or by vote of a town meeting or town in favor of terminating such membership. Said termination shall become effective at the end of the calendar year within which said termination is voted.
Mass. Gen. Laws ch. 40B, § 40B:10