No corporation may sell, mortgage, lease or otherwise encumber or dispose of any of its property (other than property which, in the judgment of the board, is neither necessary nor useful in operating and maintaining the corporation's system and which in any one year shall not exceed 10 percent in value of the value of all the property of the corporation or merchandise) unless authorized so to do by the votes of at least a majority of its members and the consent of the holders of 75 percent in amount of the bonds of such corporation then outstanding is obtained.
Ala. Code § 37-7-11 (1975)