Md. Code, Public Utilities § 17–304

The Commission is not liable for the payment of interest under this subtitle:

(1) if a proper invoice for accrued interest is not submitted within 30 calendar days after the date of the Commission’s check for payment of the amount on which the interest accrued;

(2) for more than 1 year following the 31st calendar day after the receipt date;

(3) on amounts representing unpaid interest; or

(4) if there is a dispute, as determined by the Commission, as to any material factor in the contract or purchase order.