California Code, Civil Code - CIV § 9358

(a) The public entity shall, on receipt of a stop payment notice, withhold from the direct contractor sufficient funds due or to become due to the direct contractor to pay the claim stated in the stop payment notice and to provide for the public entity's reasonable cost of any litigation pursuant to the stop payment notice.

(b) The public entity may satisfy its duty under this section by refusing to release funds held in escrow under Section 10263 or 22300 of the Public Contract Code.