Mass. Gen. Laws ch. 53, § 72: Regulations for city or town caucuses

Section 72. Each city or town committee may make reasonable regulations, consistent with law, relative to caucuses called by it and to determine membership in the party, and to restrain persons not entitled to vote at caucuses from attendance thereat or taking part therein. But no political committee shall prevent any voter from participating in a caucus of its party for the reason that the voter has supported an unenrolled candidate for political office.