Cal. Rev. & Tax. Code § 6908

(a)If the board determines that any overpayment has been made intentionally or by reason of carelessness, it shall not allow any interest thereon.

(b)If any person who has filed a claim for refund requests the board to defer action on the claim, the board, as a condition to deferring action, may require the claimant to waive interest for the period during which the person requests the board to defer action on the claim.