Okla. Stat. tit. 11 § 9-117
Appointments and promotions in the service of a statutory aldermanic city shall be made solely on the basis of merit and fitness. Removals, demotions, suspensions, and layoffs shall be made solely for the good of the service. The council may suspend for cause, by a majority vote of all its members, any officer of the city except the mayor. The council by ordinance may establish a system for appointment and removal of employees on the basis of merit. After the council establishes a merit system, it shall adopt regulations governing the organization and functioning of the system, and for the regulation of personnel matters. The ordinance establishing the merit system may not be repealed except upon the approval of a majority of the registered voters voting on the question at a special or general election in the city.
Okla. Stat. tit. 11, § 9-117