(a) Port directors shall refuse release of all plants or plant products with respect to which a notice of prohibition has been promulgated by the Secretary of Agriculture under any of the various quarantines. If an importer refuses to export a prohibited shipment immediately, the port director shall report the facts to the U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Plant Protection and Quarantine Programs and the United States attorney and withhold delivery pending advice from that Department.

(b) In case of doubt as to whether any plant or plant product is prohibited, the port director shall detain it pending advice from the Department of Agriculture.