Cal. Civil Code § 8800

(a) Except as otherwise agreed in writing by the owner and direct contractor, the owner shall pay the direct contractor, within 30 days after notice demanding payment pursuant to the contract is given, any progress payment due as to which there is no good faith dispute between them. The notice given shall comply with the requirements of Chapter 2 (commencing with Section 8100) of Title 1. (b) If there is a good faith dispute between the owner and direct contractor as to a progress payment due, the owner may withhold from the progress payment an amount not in excess of 150 percent of the disputed amount. (c) An owner that violates this section is liable to the direct contractor for a penalty of 2 percent per month on the amount wrongfully withheld, in place of any interest otherwise due. In an action for collection of the amount wrongfully withheld, the prevailing party is entitled to costs and a reasonable attorney’s fee. (d) This section does not supersede any requirement of Article 2 (commencing with Section 8810) relating to the withholding of a retention.