Ala. Code § 39-7-30
The services of the authority shall not be diminished so as to exclude from an enterprise in which the authority is engaged the furnishing of any services unless and until all bonds of the authority and interest thereon issued by the authority pursuant to this chapter shall have been finally paid and discharged, except with the consent of the holders of 75 percent in amount of such bonds then outstanding secured in whole or in part by a pledge of revenues derived from the furnishing of the services to be excluded. Thereafter, such services may be diminished and the mode or method of procedure for the diminishing of such services shall conform as nearly as may be reasonable to the provisions of this chapter relative to the manner of enlarging the services of such authority.
Ala. Code § 39-7-30 (1975)