All contracts for the construction or completion of any work or improvement, or for furnishing labor, materials or supplies shall be let to the lowest responsible bidder. The legislative body shall advertise in the city pursuant to Section 6062 of the Government Code, inviting sealed proposals for furnishing labor, materials and supplies for the proposed improvement before any contract shall be made; provided, however, that if chartered the city shall follow its charter as to making of contracts. The legislative body shall have the right to require such bonds as it may deem best from the successful bidder to insure the faithful performance of the contract, and shall also have the right to reject any and all bids.