California Code, Unemployment Insurance Code - UIC § 1113.1

An employer who, through an error caused by excusable neglect, makes an underpayment of the amount due on a report of contributions pursuant to subdivision (b) of Section 1088 shall not be liable for penalty or interest under Sections 1112, 1113, 1127 or 1129 if proper adjustment is made at the time of the filing of the quarterly report of contributions and quarterly return, for the same calendar quarter under subdivision (a) of Section 1088 and an explanation of the error is attached to the report or return.