California Code, Business and Professions Code - BPC § 9842

All work done by a service dealer shall be recorded on an invoice in such detail as is required by regulations issued by the director and shall describe all service work done and all parts supplied. If any used parts are supplied, the invoice shall clearly state that fact. One copy shall be given to the customer and one copy shall be retained by the service dealer for a period of at least three years.If a copy of the invoice is provided to the customer in an electronic format, an electronic copy of the invoice shall be retained by the service dealer for the same retention period.