Okla. Const. art. X, § 12

Special forms of taxation - Amounts - Reference to Federal taxation. The Legislature shall have power to provide for the levy and collection of license, franchise, gross revenue, excise, income, collateral and direct inheritance, legacy, and succession taxes; also graduated income taxes, graduated collateral and direct inheritance taxes, graduated legacy and succession taxes; also stamp, registration, production or other specific taxes. In the exercise of the powers provided for in this section, and notwithstanding any other provision of this Constitution, the Legislature may, with or without exceptions, modifications, or adjustments, define the amount on, in respect to, or by which any such tax or taxes are imposed or measured (a) by reference to any provisions of the laws (including administrative regulations, determinations, and interpretations) of the United States, as such laws may be or become effective at any time or from time to time; (b) by reference to any amount or amounts finally ascertained in determining amounts subject to taxation by the United States; or (c) by reference to any amount or amounts of tax finally ascertained to be payable to the United States. Amended by State Question No. 444, Legislative Referendum No. 160, adopted at election held on Aug. 27, 1968. Amendment proposed by Laws 1967, p. 689, S.J.R. No. 30.