Unemp. Ins. Code, § 1034

(a) The employer, within 60 days after the date of mailing of any statement of charges or credits and charges to the reserve account, or within an additional period not exceeding 60 days which may for good cause be granted by the director, may file with the director a written protest on any item shown thereon. The protest shall set forth the specific grounds on which it is made. No protest may be made on the ground that a claimant was ineligible for a benefit payment where the employer was notified as required by this division and any authorized regulation of the filing of a claim for the benefits or of a determination of the claimant’s eligibility therefor and the employer failed to file a timely appeal on the benefit claim, or a final decision of an administrative law judge or of the appeals board affirmed the payment of the benefits. Except as to corrections made by the director as provided in Section 1036, the contribution rate and other items shown on any such statement of charges or statement of account shall be final unless a protest is filed within the time prescribed in this section.

(b) The employer, within 30 days after the last working day of March, may file a protest on the grounds that the director did not allow voluntary unemployment insurance contributions to the reserve account in accordance with Section 976.5.