Tennessee Code Title 64. Regional Authorities § 64-3-106

(a) This chapter applies to Williamson, Rutherford and Metropolitan Nashville-Davidson counties for the purpose of implementing the programs established in this chapter, and any or all of these counties are hereby expressly authorized by the general assembly to participate in the programs established. However, prior to participation in such programs, the county legislative bodies of such counties shall express their desire to participate in the programs by means of a resolution to that effect, passed by each or all of the respective local legislative bodies of the counties involved. The resolution shall be approved by a two-thirds ( 2/3 ) vote of such legislative bodies within one hundred twenty (120) days of July 1, 1980.

(b) Any county to which this chapter applies that has elected or elects to participate in the programs authorized by the chapter may withdraw from participation therein by resolution to that effect adopted by a two-thirds ( 2/3 ) vote of the county legislative body of such county. However, such withdrawal does not relieve such county of any of its then existing obligation on account of bonds or other evidence of indebtedness incurred by such county on account of its participation in the programs of the authority, and such obligation shall continue until discharged by the county.