Unless the improvement is made by the city, contract therefor shall be let upon competitive bidding after notice is published in the official newspaper doing the city printing for a period of at least two consecutive issues. The notice shall specify that all bids shall be accompanied by a certified check payable to the order of the city clerk-treasurer in a sum not less than five percent of the amount of the bid, and no bid shall be considered unless accompanied by such a check; the notice shall also provide that the bidder shall, within ten days after the acceptance of his bid by the city council, enter into contract required by the city and furnish the bond required by the city as security on the contract, and the certified check shall be retained by the city clerk-treasurer until the required bond has been furnished and the contract has been entered into, and shall be forfeited to the city if the contract is not entered into and the bond is not furnished within the time specified in this section, absolutely and without order of the city council or any declaration of forfeiture. (Ord. 1337, §5, 1980).