46 USC 60501 - Vessels allowed to import

(a) In General.— 
Except as otherwise provided by treaty, goods may be imported into the United States from a foreign port or place only in
(1) a vessel of the United States; or
(2) a foreign vessel owned only by citizens or subjects of the country
(A) in which the goods are grown, produced, or manufactured; or

view counter
(B) from which the goods can only be, or most usually are, first shipped for transportation.
(b) Exception for Vessels of Countries Not Maintaining Similar Restrictions.— 
Subsection (a) does not apply to a vessel of a foreign country that does not maintain a similar restriction against United States documented vessels.
(c) Exception for Vessels Becoming Documented.— 
Subsection (a) does not apply to a vessel that
(1) is owned only by citizens of the United States; and
(2) after entering a port of the United States, becomes documented as a vessel of the United States before leaving that port.
(d) Seizure and Forfeiture.— 
If goods are imported in violation of this section, the goods and the vessel in which they are imported, along with its equipment and other cargo, may be seized by and forfeited to the United States Government.