Tenn. Code Ann. § 5-14-109

Except in emergencies, no order for delivery on a contract or open market order for supplies, materials, equipment or contractual services for any county department or agency shall be awarded unless it shall be first certified by the director of accounts and budgets, or other county official or employee in charge of the central accounting records of the county that the unencumbered balance in the appropriation chargeable with such purchase in excess of all unpaid obligations, is sufficient to defray the entire cost of such order or contract.