Mass. Gen. Laws ch. 167, § 15E
(b) With respect to bonds, the obligations shall be those of a railroad incorporated in the United States or any state doing business principally within the United States and shall contain an unconditional promise to pay the interest on the bonds regularly and to pay the principal at a specified date. This promise may be modified, if at all, only by a vote of holders of at least 75 per cent in amount of the bonds.
Not more than 20 per cent of the assets of the entity shall be invested in the railroad obligations.