Tenn. Code Ann. § 7-82-303

No utility district created prior to March 4, 1947, under the terms and provisions of this chapter, shall undertake to render or obligate itself to render services other than those for the furnishing of water, sewer, sewage disposal, fire protection, natural gas or artificial gas, unless and until it shall first have obtained the consent in writing of subscribers representing seventy-five percent (75%) in number of the total subscribers to the existing services furnished by the utility district at the time such written consents are obtained. The determination by the board of commissioners of any such district as to the percentage represented by the written consent of such subscribers shall be conclusive, that no such district may furnish natural gas service to any area now actually served by a private company.