19 USC 1448 - Unlading

(a) Permits and preliminary entries 
Except as provided in section 1441 of this title (relating to vessels not required to enter or clear), no merchandise, passengers, or baggage shall be unladen from any vessel required to make entry under section 1434 of this title, or vehicle required to report arrival under section 1433 of this title, until entry of such vessel or report of the arrival of such vehicle has been made and a permit for the unlading of the same issued or transmitted pursuant to an electronic data interchange system by the Customs Service. After the entry of any vessel or report of the arrival of any vehicle, the Customs Service may issue a permit, electronically pursuant to an authorized electronic data interchange system or otherwise, to the master of the vessel, or to the person in charge of the vehicle, to unlade merchandise or baggage, but except as provided in subdivision (b) of this section merchandise or baggage so unladen shall be retained at the place of unlading until entry therefor is made and a permit for its delivery granted, and the owners of the vessel or vehicle from which any imported merchandise is unladen prior to entry of such merchandise shall be liable for the payment of the duties accruing on any part thereof that may be removed from the place of unlading without a permit therefor having been issued. The owner or master of any vessel or vehicle, or agent thereof, shall notify the Customs Service of any merchandise or baggage so unladen for which entry is not made within the time prescribed by law or regulation. The Secretary shall by regulation prescribe administrative penalties not to exceed $1,000 for each bill of lading for which notice is not given. Any such administrative penalty shall be subject to mitigation and remittance under section 1618 of this title. Such unentered merchandise or baggage shall be the responsibility of the master or person in charge of the importing vessel or vehicle, or agent thereof, until it is removed from the carriers control in accordance with section 1490 of this title.
(b) Special delivery permit 
The Secretary of the Treasury is authorized to provide by regulations for the issuing of special permits for delivery, prior to formal entry therefor, of perishable articles and other articles, the immediate delivery of which is necessary.