California Code, Health and Safety Code - HSC § 5010

All works acquired or constructed under this chapter where the expense involved exceeds five hundred dollars, shall be done by contract which shall be awarded to the lowest responsible bidder as provided in this chapter. If the bonds are purchased by the Reconstruction Finance Corporation or other fiscal agency of the United States on condition or request that the governing body have the work performed by day labor instead of by contract, the governing body may comply with the condition or request and the work need not be done by contract.