CA Civ Code Section 8818

If an owner or direct contractor does not make a retention payment within the time required by this article:

(a)

The owner or direct contractor is liable to the person to which payment is owed for a penalty of 2 percent per month on the amount wrongfully withheld, in place of any interest otherwise due.

(b)

In an action for collection of the amount wrongfully withheld, the prevailing party is entitled to costs and reasonable attorney’s fees.