California Code, Education Code - EDC § 24617

(a) To recover an amount overpaid under this part or Part 14 (commencing with Section 26000), as determined pursuant to Section 24616.2, the system shall correct the benefit, annuity, or refund, and the corrected monthly allowance payable under the Defined Benefit Program or the corrected annuity benefit payable under the Defined Benefit Supplement Program or the Cash Balance Benefit Program may be reduced by no more than 15 percent if the amount overpaid was due to inaccurate information or nonsubmission of information by, or on behalf of, a recipient of the allowance or annuity benefit, not including an error by the system, a county superintendent of schools, or an employer.

(b) This section does not apply to the collection of overpayments due to fraud or intentional misrepresentation of facts by the recipient of the allowance or benefit.