Cal. Rev. & Tax. Code § 19361

In the case of an overpayment of tax imposed by Section 18662 or 18666, refund or credit shall be made to the employer or to the withholding agent, as the case may be, only to the extent that the amount of the overpayment was not deducted and withheld by the employer or withholding agent. No interest shall be allowed on the overpayment.