N.C. Gen. Stat. § 159-93
The State of North Carolina does pledge to and agree with the holders of any revenue bonds or revenue bond anticipation notes heretofore or hereafter issued by the State or any municipality in this State that so long as any such bonds or notes are outstanding and unpaid the State will not limit or alter the rights vested in the State or the municipality at the time of issuance of the bonds or notes to establish, maintain, revise, charge, and collect such rates, fees, rentals, tolls, and other charges for the use, services, facilities, and commodities of or furnished by the revenue bond project in connection with which the bonds or notes, or bonds or notes refunded by the bonds or notes, were issued as shall produce revenues at least sufficient with other available funds to meet the expense of maintenance and operation of and renewal and replacements to such project, including reserves therefor, to pay when due the principal, interest, and redemption premiums (if any) of the bonds or notes, and to fulfill the terms of any agreements made with the bondholders or noteholders, nor will the State in any way impair the rights and remedies of the bondholders or noteholders until the bonds or notes and all costs and expenses in connection with any action or proceedings by or on behalf of the bondholders or noteholders, are fully paid, met, and discharged.
N.C. Gen. Stat. § 159-93