19 CFR 151.11: Request for samples or additional examination packages after release of merchandise.

If an authorized CBP official requires samples or additional examination packages of merchandise which has been released from CBP custody, an authorized CBP official will send the importer a written request, on Customs Form 28, or its electronic equivalent, Request for Information, or other appropriate form, to submit the necessary samples or packages. If the request is not promptly complied with, an authorized CBP official may make a demand under the bond for the return of the necessary merchandise to CBP custody in accordance with § 141.113 of this chapter. For purposes of determining admissibility, representatives of the Food and Drug Administration may obtain samples of any food, drug, device, or cosmetic, the importation of which is governed by section 801 of the Federal Food, Drug, and Cosmetic Act, as amended (21 U.S.C. 381).