Mass. Gen. Laws ch. 161B § 14
An authority described in section two of this chapter shall be deemed to be established (a) after twenty per cent of the votes on the advisory board have recorded themselves in favor of calling a meeting to vote on the establishment of the authority, (b) notice of the meeting has been sent by a member municipality of the authority to every other member municipality at least two weeks prior to said meeting and (c) the advisory board has sent the governor written notification that the advisory board has voted to establish the authority; provided that such notification shall not be given except after a majority of municipalities have voted to establish the authority.
The membership of the authority upon its establishment as provided in this section shall consist of those cities and towns which affirmatively vote for the formation of the authority as provided in the first paragraph. Nothing contained in this section shall prevent any city or town, including a city or town which did not vote for the formation of the authority under the first paragraph from joining an authority subsequent to the formation thereof.
Mass. Gen. Laws ch. 161B, § 14