O.C.G.A. § 32-4-117 (2019)

(a) A municipality may require that each bid on a particular contract, as a prerequisite to the bid being considered, be accompanied by a proposal guaranty in the form of a certified check or other acceptable security payable to the municipality for an amount deemed by the municipality in the public interest necessary to ensure that the successful bidder will execute the contract on which he bid.

(b) Such proposal guaranty will be returned to a bidder upon receipt by the municipality of the bidder’s written withdrawal of his bid if such receipt is before the time scheduled for the opening of bids. Upon the determination by the municipality of the lowest reliable bidder, the municipality will return proposal guaranties to all bidders except the proposal guaranty of the lowest reliable bidder. If no contract award is made within 30 days after the date set for the opening of bids, all bids shall be rejected and all proposal guaranties shall be returned unless the municipality and the successful bidder agree in writing to a longer period of time.