California Code, Civil Code - CIV § 8522

(a) Except as provided in subdivision (b), on receipt of a stop payment notice an owner shall withhold from the direct contractor or from any person acting under authority of a direct contractor a sufficient amount due or to become due to the direct contractor to pay the claim stated in the notice.

(b) The owner may, but is not required to, withhold funds if the owner has previously recorded a payment bond under Section 8600. If the owner does not withhold funds, the owner shall, within 30 days after receipt of the stop payment notice, give notice to the claimant that a payment bond has been recorded and provide the claimant a copy of the bond. The notice shall comply with the requirements of Chapter 2 (commencing with Section 8100) of Title 1.