Okla. Stat. tit. 36, § 6002

No form or plan of insurance covering any group or combination of persons or risks shall be written or delivered within or outside of this state to cover Oklahoma persons or risks at any preferred rate or form other than that offered to persons not in such group, and the public generally, unless such form, plan or policy and the rates or premiums to be charged therefor have been submitted to and filed or approved by the Insurance Commissioner.