California Code, Vehicle Code - VEH § 8058

(a) The department shall charge interest on any underpaid fees due under this article, at the rate of 1 percent per month of the underpaid portion of the fees, commencing on the date the underpaid portion of the fees were originally due and accruing monthly until paid.

(b) Interest charged under subdivision (a) shall continue to accumulate during any disputation of the underpaid fees or any hearing regarding the underpaid fees.  During any disputation or hearing, the registrant may pay the underpaid fees and other charges to avoid additional interest charges and may request a refund of any overpaid fees after final review.

(c) For any underpaid fees, the department may impose a penalty of fifty dollars ($50) or 10 percent of the underpaid fees, whichever is greater, commencing on the date the underpaid fees were determined to be due.

(d) For the purposes of this section, “underpaid fees” include additional vehicle registration, weight, and license fees found to be due to this state.

(e) The director shall have discretion to apply subdivision (b) of Section 9562 instead of subdivision (c) of this section.

(f) The penalty structure set forth in Sections 9554 and 9554.5 shall apply in place of the provisions of this section in those cases where there is a violation of Section 4000, 4000.4, 4002, 4003, 4004, 4004.5, or 4156 for commercial registration that is not apportioned pursuant to Section 8050.