19 CFR § 4.1 - Boarding of vessels.
(a) Every vessel arriving at a CBP port will be subject to such supervision while in port as the port director considers necessary. The port director may detail CBP officers to remain on board a vessel to secure enforcement of the requirements set forth in this part. CBP may determine to board as many vessels as considered necessary to ensure compliance with the laws it enforces.
(1) No person, with or without the consent of the master, except a pilot in connection with the navigation of the vessel, personnel from another vessel in connection with the navigation of an unmanned barge, an officer of CBP or the Coast Guard, an immigration or health officer, an inspector of the Animal and Plant Health Inspection Service of the U.S. Department of Agriculture, or an agent of the vessel or consular officer exclusively for purposes relating to customs formalities, shall go on board any vessel arriving from outside the customs territory of the United States without permission of the port director or the CBP officer in charge until the vessel has been taken in charge by a CBP officer.
(2) A person may leave the vessel for the purpose of reporting its arrival as required by law (see § 4.2), but no other person, except those designated in paragraph (b)(1) of this section, shall leave any vessel arriving from outside the customs territory of the United States, with or without the consent of the master, without the permission of the port director or the CBP officer in charge until the vessel has been properly inspected by CBP and brought into the dock or anchorage at which cargo is to be unladen and until all passengers have been landed from the vessel (19 U.S.C. 1433).
(3) Every person permitted to go on board or to leave without the consent of a CBP officer under the provisions of this paragraph shall be subject to CBP and quarantine regulations.
(4) The master of any vessel shall not authorize the boarding or leaving of his vessel by any person in violation of this paragraph.
(c) Persons seeking to board an incoming vessel after it has been inspected by the quarantine authorities and taken in charge by a CBP officer must comply with any applicable Coast Guard regulations regarding the Transportation Worker Identification Credential (TWIC)/personal identification requirements as prescribed in 33 CFR 101.105 and 101.514-515.
(d) No person in charge of a tugboat, rowboat, or other vessel shall bring such conveyance alongside an incoming vessel heretofore described and put on board thereof any person, except as authorized by law or regulations.