Ala. Code § 39-7-26
The State of Alabama does hereby pledge to and agree with the holders of bonds issued by an authority pursuant to this chapter that the state will not limit or alter the rights and powers hereby vested in an authority incorporated under this chapter to fix and collect such rates and charges as may be necessary or advisable in order to produce sufficient revenue to meet all the expenses of maintenance and operation and to fulfill the terms of any agreements made with the holders of such bonds or in any way impair the rights and remedies of the holders of such bonds, until such bonds together with interest thereon and interest on any unpaid installments of interest, and all costs and expenses in connection with any civil actions or proceedings by or on behalf of such bondholders are fully paid and discharged.
Ala. Code § 39-7-26 (1975)