Tenn. Code Ann. § 6-22-129

No contract liability shall be incurred without previous authority of law or ordinance, but the board of commissioners may, by ordinance, empower the proper officials to pay out money or incur contract liability for the city for the necessary preservation of the city's credit, or in other extreme emergency, under such restrictions as may be provided in the ordinance; provided, that any such liability shall mature not later than one (1) year from the date of its incurrence.