19 USC 1581 - Boarding vessels

(a) Customs officers 
Any officer of the customs may at any time go on board of any vessel or vehicle at any place in the United States or within the customs waters or, as he may be authorized, within a customs-enforcement area established under the Anti-Smuggling Act [19 U.S.C. 1701 et seq.], or at any other authorized place, without as well as within his district, and examine the manifest and other documents and papers and examine, inspect, and search the vessel or vehicle and every part thereof and any person, trunk, package, or cargo on board, and to this end may hail and stop such vessel or vehicle, and use all necessary force to compel compliance.
(b) Officers of Department of the Treasury 
Officers of the Department of the Treasury and other persons authorized by such department may go on board of any vessel at any place in the United States or within the customs waters and hail, stop, and board such vessel in the enforcement of the navigation laws and arrest or, in case of escape or attempted escape, pursue and arrest any person engaged in the breach or violation of the navigation laws.
(c) Penalty for presenting forged, altered, or false documents 
Any master of a vessel being examined as herein provided, who presents any forged, altered, or false document or paper to the examining officer, knowing the same to be forged, altered, or false and without revealing the fact shall, in addition to any forfeiture to which in consequence the vessel may be subject, be liable to a fine of not more than $5,000 nor less than $500.
(d) Penalty for failure to stop at command 
Any vessel or vehicle which, at any authorized place, is directed to come to a stop by any officer of the customs, or is directed to come to a stop by signal made by any vessel employed in the service of the customs and displaying proper insignia, shall come to a stop, and upon failure to comply a vessel or vehicle so directed to come to a stop shall become subject to pursuit and the master, owner, operator, or person in charge thereof shall be liable to a penalty of not more than $5,000 nor less than $1,000.
(e) Seizure of vessel or merchandise 
If upon the examination of any vessel or vehicle it shall appear that a breach of the laws of the United States is being or has been committed so as to render such vessel or vehicle, or the merchandise, or any part thereof, on board of, or brought into the United States by, such vessel or vehicle, liable to forfeiture or to secure any fine or penalty, the same shall be seized and any person who has engaged in such breach shall be arrested.
(f) Duty of customs officers to seize vessel 
It shall be the duty of the several officers of the customs to seize and secure any vessel, vehicle, or merchandise which shall become liable to seizure, and to arrest any person who shall become liable to arrest, by virtue of any law respecting the revenue, as well without as within their respective districts, and to use all necessary force to seize or arrest the same.
(g) Vessels deemed employed within United States 
Any vessel, within or without the customs waters, from which any merchandise is being, or has been, unlawfully introduced into the United States by means of any boat belonging to, or owned, controlled, or managed in common with, said vessel, shall be deemed to be employed within the United States and, as such, subject to the provisions of this section.
(h) Application of section to treaties of United States 
The provisions of this section shall not be construed to authorize or require any officer of the United States to enforce any law of the United States upon the high seas upon a foreign vessel in contravention of any treaty with a foreign government enabling or permitting the authorities of the United States to board, examine, search, seize, or otherwise to enforce upon said vessel upon the high seas the laws of the United States except as such authorities are or may otherwise be enabled or permitted under special arrangement with such foreign government.