(a) Any insurer that fails to pay any prepayment within the time required shall pay a penalty of 10 percent of the amount of the required prepayment, plus interest at the modified adjusted rate per month, or fraction thereof, established pursuant to Section 6591.5, from the due date of the prepayment until the date of payment but not for any period after the due date of the annual tax. Assessments of prepayment deficiencies may be made in the manner provided by deficiency assessments of the annual tax.
(b) This section shall become operative on July 1, 2012.