Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 180, § 19

No fine or notice of intention to impose a fine by any union or any other association, incorporated or unincorporated, or by any authorized representative thereof, upon any member, according to the rules to which such member has agreed to conform, shall be held to be unlawful or coercive as to such member or as to any other person; provided, that such fine is reasonable in amount and is for a legal purpose.