Tenn. Code § 65-4-308
In case of default in the payment of any fee, or part thereof, when the same shall become due, as provided in § 65-4-306, any such public utility in default shall be liable for a penalty of ten percent (10%) per month or fraction thereof, on the amount of the fee, which may be recovered by suit of the state for every month it remains in default, and any such penalty, when collected, shall be deposited into the state treasury as a part of the utilities account; provided, that out of any such penalty, the commission may employ and pay counsel, who shall have power to institute suit in any court of competent jurisdiction for the recovery of such penalty, but in no event shall anything more than the penalty be allowed to such counsel for making such collections.
T.C.A. § 65-4-308