Tenn. Code § 8-25-310
The state treasurer, with the approval of the commissioner of finance and administration, may adopt a new feature to the plan that would provide for an alternative social security replacement plan that satisfies the requirements of § 3121(b)(7)(F) of the Internal Revenue Code (26 U.S.C. § 3121(b)(7)(F)), as may be amended, and any rules and regulations promulgated thereunder for any classes of state employees, including employees of institutions of higher education, whose service is not covered by an agreement entered into under § 8-38-103. Any such plan may require the withholding as deferred compensation from the wages otherwise payable to those employees of up to seven and one-half percent (7½%) of wages, as the term "wages" is defined for social security purposes, or such other amount as may be required as an alternative to social security contributions.
T.C.A. § 8-25-310