California Code, Public Contract Code - PCC § 6109

(a) A public entity, as defined in Section 1100, may not permit a contractor or subcontractor who is ineligible to bid or work on, or be awarded, a public works project pursuant to Section 1777.1 or 1777.7 of the Labor Code to bid on, be awarded, or perform work as a subcontractor on, a public works project.  Every public works project shall contain a provision prohibiting a contractor from performing work on a public works project with a subcontractor who is ineligible to perform work on the public works project pursuant to Section 1777.1 or 1777.7 of the Labor Code.

(b) Any contract on a public works project entered into between a contractor and a debarred subcontractor is void as a matter of law.  A debarred subcontractor may not receive any public money for performing work as a subcontractor on a public works contract, and any public money that may have been paid to a debarred subcontractor by a contractor on the project shall be returned to the awarding body.  The contractor shall be responsible for the payment of wages to workers of a debarred subcontractor who has been allowed to work on the project.