California Code, Public Contract Code - PCC § 22154

(a) All businesses shall certify in writing to the contracting officer, or his or her representative, the minimum, if not exact, percentage of postconsumer material in the products, materials, goods, or supplies being offered or sold to any local public entity.

(b) With respect to printer or duplication cartridges that comply with the requirements of subdivision (e) of Section 12156, the certification required by this section shall specify that the cartridges so comply.

(c) A local public entity may waive the certification requirement if the percentage of postconsumer material in the products, materials, goods, or supplies can be verified in a written advertisement, including, but not limited to, a product label, a catalog, or a manufacturer or vendor Internet Web site.