Cal. Unemployment Insurance Code § 976.5

(a) Except as provided in subdivision (b), in addition to other contributions required by this division, every employer, except an employer to which subdivision (c) is applicable, may submit a voluntary unemployment insurance contribution for the purpose of redetermining its unemployment insurance contribution rate. No redetermination of a contribution rate shall be made unless the voluntary contribution is submitted as required in subdivision (c) of Section 1110. No redetermination shall reduce an employer’s unemployment insurance contribution rate by more than three rates as provided in Section 977. (b) This section shall not be operative in calendar years in which Contribution Rate Schedules E and F in Section 977 are in effect, or in calendar years to which the emergency solvency surcharge provided in Section 977.5 is in effect. (c) This section does not apply to any of the following: (1) An employer not eligible for a contribution rate other than that provided pursuant to Section 982 or subdivision (c) of Section 977. (2) An employer with a negative reserve account balance on the computation date. (3) An employer who was notified prior to September 1 of any unpaid amount owed to the department which is not the subject of a timely petition for reassessment pending before the appeals board on September 30 preceding the year to which a contribution rate is applicable.