Mass. Gen. Laws ch. 161 § 66
Two domestic companies, whose railways connect with or intersect each other or together form a continuous line, may contract that either company shall perform all the transportation upon and over the whole or any part of the railway of the other; or any such company may lease its franchise, property and railway to any other such company; but the facilities for travel on either of the railways of said companies shall not be thereby diminished or the rates of fare increased. Such contract or lease shall not be valid or binding until its terms have been agreed to by a majority of the directors, and have been approved, at meetings called therefor, by a vote of a majority in interest of the stockholders of each of said companies, and by the department as required by section fifty-four of chapter one hundred and fifty-nine. The income arising from such contracts or leases shall be subject to the provisions of law relative to the reduction of fares in the same manner as that arising from the use of the railways. Such railways shall be considered as connecting with or intersecting each other, or forming a continuous line, if one of them connects with or intersects or forms a continuous line with a railway leased to or operated by the other under a contract authorized by this section.
Mass. Gen. Laws ch. 161, § 66