Ala. Code § 45-8A-23.183

Any city improvement costing more than five hundred dollars ($500) shall be executed by contract. All such contracts for more than five hundred dollars ($500) shall be awarded to the lowest responsible bidder after such public notice and competition as may be prescribed by ordinance, provided the city manager 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 city manager.