Okla. Stat. tit. 68 § 2385.15
The administration of the provisions of Sections 2385.1 through 2385.19, inclusive, is vested in the Tax Commission. All forms necessary and proper for the enforcement of such provisions shall be prescribed and furnished by the Tax Commission, and the Tax Commission may promulgate rules and regulations to enforce such provisions, if not inconsistent with such provisions, as may be reasonably necessary to make practical the administration thereof, including the use of a bracket or tables closely approximating the amount required to be withheld under the provisions of Section 2385.2. In cases where employers have difficulty in determining the exact amount of wages earned by employees in this State, the Tax Commission may enter into an agreement with such employers as may be deemed most practical.
Okla. Stat. tit. 68, § 2385.15