California Business & Professions Code Section 7159.6
Extra work or change order; enforceability conditions
(a) An extra work or change order is not enforceable against a buyer unless the change order sets forth all of the following:
(1) The scope of work encompassed by the order.
(2) The amount to be added or subtracted from the contract.
(3) The effect the order will make in the progress payments or the completion date.
(b) The buyer may not require a contractor to perform extra or change-order work without providing written authorization.
(c) Failure to comply with the requirements of this section does not preclude the recovery of compensation for work performed based upon legal or equitable remedies designed to prevent unjust enrichment.
(d) This section shall become operative on January 1, 2006.