Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 160, § 210

A railroad corporation shall not, at any time, charge, demand or receive a greater sum for transportation by it of freight from any point of origin, for the same distances and under like conditions, on any lines operated by it or in connection with it, to the port of Boston for export to foreign countries, than is at the time received by it for transportation of the like class and quantity of freight to any other port reached by its lines for export to foreign countries; or charge, demand or receive, a greater sum for transportation for the same distance and under like conditions from the port of Boston of freight from foreign countries through said port of Boston to any point on any lines operated by it or in connection with it then is at the time received by it for transportation of the like class and quantity of freight through any other port on its lines to the same point; provided, that if the aforesaid provisions of this section shall conflict with any regulations made by act of congress this section shall be null and void so far as it conflicts therewith; and provided, further, that nothing herein contained shall justify the charging of the same rate for freight for export or import through any other port reached by its lines where the mileage from the point of receipt or delivery is less to the port of Boston than to the port in question, in which case the rate through Boston shall be proportionately less.