California Code, Revenue and Taxation Code - RTC § 50112

(a) Any feepayer who fails to pay any fee to the state or any amount of fee required to be collected and paid to the state, except amounts of determinations made by the board under Article 2 (commencing with Section 50113) within the time required shall pay a penalty of 10 percent of the amount of the fee, together with interest on that fee at the modified adjusted rate per month, or fraction thereof, established pursuant to Section 6591.5, from the date on which the fee became due and payable until the date of payment.

(b) Any feepayer who fails to file a return in accordance with the due date set forth in Section 50109 or the due date established by the board in accordance with Section 50110, shall pay a penalty of 10 percent of the amount of the fee with respect to the period for which the return is required.

(c) The penalties imposed by this section shall be limited to a maximum of 10 percent of the fee for which the return is required for any one return.