Tennessee Code Title 50. Employer and Employee § 50-1-204

It is unlawful for any person, firm, corporation or association of any kind operating in this state to execute an agreement with a union or employee organization of any kind that includes a maintenance of membership clause prohibiting employees from withdrawing from a union or employee organization prior to the agreement's expiration. This section shall not apply to a city, town, municipality or county, including a county having a metropolitan form of government.