Okla. Stat. tit. 68, § 2385

Specified tax return preparers - Electronic filing. Any specified tax return preparer shall file all individual income tax returns prepared by such preparer by electronic means. The term “specified tax return preparer” shall have the same meaning as provided in Section 6011 of the Internal Revenue Code of 1986, as amended. The preparation of a substantial part of a return or claim for refund is treated as if it were the preparation of the entire return or claim for refund. This section shall apply to all returns filed after December 31, 2010.