Okla. Stat. tit. 74 § 255
The heads of the departments except as otherwise herein provided are hereby authorized and empowered to appoint persons to hold positions created in their respective departments. The persons so appointed shall hold office at the will of such state officer and in the case of all boards and commissioners, such board or commission shall, by vote thereof, except as otherwise provided, appoint persons to hold positions created under such boards or commissions by this act, and the persons so appointed shall hold office at the will of such officer, boards or commissions making the appointment, provided that any board or commission may authorize the secretary of such board or commission to make the appointment.
Provided further, that it shall be unlawful for the heads of any department, or any departments, except institutions of higher learning and state hospitals, the State Health Department, the Highway Department in the employment of engineers and technicians, schools for individuals with intellectual disabilities and State Veterans Facilities as pertains to doctors, dentists, nurses and other trained technicians, to employ in any way any person who is not a citizen of the United States, and repealing all laws in conflict herewith. The provisions of this act shall in no way be interpreted to repeal any provision of the laws heretofore enacted creating the Merit System of the State of Oklahoma.
Okla. Stat. tit. 74, § 255