Ala. Code § 45-51A-33.168

Any city improvement costing more than two thousand dollars ($2,000) shall be executed by contract except where such improvement is authorized by the council to be executed directly by a city department in conformity with detailed plans, specifications, and estimates. All such contracts for more than two thousand dollars ($2,000) shall be awarded to the lowest responsible bidder after such public notice and competition as may be prescribed by resolution or ordinance, provided the mayor shall have the power to reject all bids and advertise again. Alterations in any contract may be made when authorized by the council upon the written recommendation of the mayor.