California Code, Labor Code - LAB § 3800

(a) Every county or city which requires the issuance of a permit as a condition precedent to the construction, alteration, improvement, demolition, or repair of any building or structure shall require that each applicant for the permit sign a declaration under penalty of perjury verifying workers' compensation coverage or exemption from coverage, as required by Section 19825 of the Health and Safety Code.

(b) At the time of permit issuance, contractors shall show their valid workers' compensation insurance certificate, or the city or county may verify the workers' compensation coverage by electronic means.