A municipality has statutory authority to enact zoning regulations for territory adjacent to but outside of its boundaries if that area has no zoning already in force.  T.C.A. § 13-7-302.  In order to enact zoning outside its municipal boundaries, the municipal planning commission must also be designated as the regional planning commission (T.C.A. § 13-3-102), and the municipality must file notice of intent with the county mayor at least six (6) months before the final enactment of the ordinance.  T.C.A. § 13-7-303.  If the county subsequently adopts zoning covering that territory, the municipal zoning is automatically superseded and repealed. T.C.A. § 13-7-306.  According to the comprehensive growth planning law, a city may not zone outside its urban growth boundary once this boundary is in place.  T.C.A. § 6-58-106(d).