Okla. Stat. tit. 68 § 2385.17
Any amount withheld or paid by estimate in excess of the amount due shown by a return filed by any employee shall be refunded to said employee. The Tax Commission shall prescribe regulations providing for the crediting against the estimated income tax for any taxable year of the amount determined by the taxpayer or Tax Commission to be an overpayment of the income tax for a preceding taxable year. In order to obtain a credit against the tax due or a refund, said employee shall attach to his return a legible copy of the withholding certificate required to be furnished to said employee by his employer, as provided for by Section 2385.3 of this title. The Tax Commission may delay making any refund until such time as the claim may be verified by audit, or if the employee is delinquent in the filing of prior returns. The making of any refund shall not be a conclusive finding of the tax due by any individual but shall be made subject to the future audit of his return and the determination of his liability.
Okla. Stat. tit. 68, § 2385.17