Mass. Gen. Laws ch. 159 § 14
Whenever the department shall be of opinion, after a hearing had upon its own motion or upon complaint, that any of the rates, fares or charges of any common carrier for any services to be performed within the commonwealth, or the regulations or practices of such common carrier affecting such rates, are unjust, unreasonable, unjustly discriminatory, unduly preferential, in any wise in violation of any provision of law, or insufficient to yield reasonable compensation for the service rendered, the department shall determine the just and reasonable rates, fares and charges to be charged for the service to be performed, and shall fix the same by order to be served upon every common carrier by whom such rates, fares and charges or any of them are thereafter to be observed. Every such common carrier shall obey every requirement of every such order served upon it, and do everything necessary or proper in order to secure absolute compliance with every such order by all its officers, agents and employees. If, upon investigation, the department finds that in any case it is consistent with the public interests to authorize a common carrier to make its charge for transportation less for a longer than for a shorter distance, the department may grant such authority and may from time to time modify or revoke the same.
If complaint is made to the department concerning any rate, fare or charge demanded and collected by any railroad corporation for any service performed and the department finds after hearing and investigation that an unjustly discriminatory rate, fare or charge has been collected for any service, the department may order the railroad corporation which has collected the same to make due reparation to the person who has paid the same, with interest from the date of the payment of such unjustly discriminatory amount; but such order or reparation shall cover only payments made within two years before the date of filing the petition seeking to have reparation ordered. Such order may be made without formal hearing whenever the railroad corporation affected shall assent in writing thereto, or file or join in a petition therefor, but in no case shall any such order be made until the department shall be satisfied by such investigation as may be necessary that the rate, fare or charge collected was in fact unjustly discriminatory.
Mass. Gen. Laws ch. 159, § 14