CA Civ Code Section 9456

(a)

A stop payment notice takes priority over an assignment by a direct contractor of any amount due or to become due pursuant to a public works contract, including contract changes, whether made before or after the giving of a stop payment notice, and the assignment has no effect on the rights of the claimant.

(b)

Any garnishment of an amount due or to become due pursuant to a public works contract by a creditor of a direct contractor under Article 8 (commencing with Section 708.710) of Chapter 6 of Division 2 of Title 9 of Part 2 of the Code of Civil Procedure and any statutory lien on that amount is subordinate to the rights of a claimant.