CA Rev & Tax Code Section 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.