District of Columbia Code Division V. Local Business Affairs § 34-304. Excessive charges a complete defense in suit to collect for gas or electricity furnished.

If it be alleged and established in an action brought in any court for the collection of any charge for gas or electricity that a price has been demanded in excess of that fixed by the Commission or by statute no recovery shall be had therein, but the fact that such excessive charges have been made shall be a complete defense to such action.