Cal. Unemp. Ins. Code § 1037

If a protest involving the contribution rate is pending when any contribution to which such rate relates is due, the employer shall pay the contribution at the rate shown in the statement furnished by the director. Such a protest, however, shall constitute a claim for refund under Article 9 of this chapter, and if a final determination on the protest reduces the contribution rate the amount of overpayment shall be promptly credited or refunded as provided in that article.