California Code, Unemployment Insurance Code - UIC § 13040

(a) An employer shall use the exemption certificate filed by the employee with the employer in such form and containing such information as the department may prescribe, for determining the number of withholding exemptions to be allowed in computing the tax required to be deducted and withheld under Section 13020. However, if the employer cannot determine the employee's marital status from the exemption certificate the employee shall be considered unmarried.

(b) No withholding exemptions shall be allowed until the employee files a new withholding exemption certificate if the department finds that the withholding exemption certificate filed under this division does not properly reflect the number of exemptions allowable and so advises the employer in writing.