California Code, Civil Code - CIV § 8542

(a) If funds are withheld pursuant to a stop payment notice given to a construction lender by a direct contractor or subcontractor, the direct contractor or subcontractor may recover only the net amount due the direct contractor or subcontractor after deducting any funds that are withheld by the construction lender pursuant to the claims of subcontractors and material suppliers that have given a stop payment notice for work done on behalf of the direct contractor or subcontractor.

(b) In no event is the construction lender required to withhold, pursuant to a stop payment notice, more than the net amount provided in subdivision (a).  Notwithstanding any other provision of this chapter, a construction lender is not liable for failure to withhold more than that net amount on receipt of a stop payment notice.