Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 156D, § 6.27

(a) The articles of organization, bylaws, an agreement among shareholders or an agreement between shareholders and the corporation may impose restrictions on the transfer or registration of transfer of shares of the corporation. A restriction shall not affect shares issued before the restriction was adopted unless the holders of the shares are parties to the restriction agreement or voted in favor of the restriction, or unless the restriction is set forth in an amendment to the articles of organization or bylaws approved by the holders of that percentage of each voting group of the outstanding shares required for the approval of an amendment of the articles of organization containing the restriction.

(b) A restriction on the transfer or registration of transfer of shares is valid and enforceable against the holder or a transferee of the holder if the restriction is authorized by this section and its existence is noted conspicuously on the front or back of the certificate or is contained in the information statement required by subsection (b) of section 6.26. Unless so noted, a restriction is not enforceable against a person without knowledge of the restriction.

(c) A restriction on the transfer or registration of transfer of shares is authorized:

(d) A restriction on the transfer or registration of transfer of shares may, without limitation:

(e) For purposes of this section, “shares” includes a security convertible into or carrying a right to subscribe for or acquire shares.