California Code, Education Code - EDC § 26302

(a) If more or less than the contributions required by this part are paid to the plan based on salary paid to a participant, proper adjustment shall be made by the employer within 60 days of discovery or of notification by the system, and any contributions deducted in error from the participant's salary shall be returned to the participant by the employer within the same time period.

(b) The board shall, in accordance with regulations, assess penalties for late or improper adjustments pursuant to Section 26301.  These penalties shall be assessed at a rate equal to the penalties imposed under subdivision (b) of Section 26301 and shall be deemed to be interest earned in the year in which the penalty is received.