Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 164, § 94D

No gas or electric company shall collect from a customer on account of his failure to pay any bill due for gas or electricity furnished to him for domestic purposes any charges as, or in the nature of, a penalty; provided, that nothing herein shall prevent the collection of any amount allowable as a discount from such a bill in the event of its payment within a period specified therein, if the right to such discount has been forfeited by failure so to pay such bill.

No gas or electric company shall collect from the commonwealth or any city, town, county or political subdivision thereof, on account of its failure to pay any bill due for gas or electricity furnished to the commonwealth, or any city, town, county or political subdivision thereof, any charges as, or in the nature of, a penalty until the expiration of fifty-five days from the date of such bill; provided, that nothing herein shall prevent the collection of any amount allowable as a discount from such a bill in the event of its payment within a period specified therein, if the right to such a discount has been forfeited by failure so to pay such bill.