In Article 1, Section 8 of the US Constitution, where the powers of Congress are enumerated, there is included an obscure power to grant "letters of marque and reprisal". Letters of marque and reprisal are authorizations for private citizens to engage in acts of piracy against a foreign nation, transforming pirates into "privateers". In the 18th century, this was often used as a low-level act of hostility against an enemy nation, instead of (or as a supplement to) a full war. An 1856 treaty called the Declaration of Paris banned letters of marque and reprisal, which the United States has generally abided by, but has never actually been a signatory. The Confederate States of America did authorize some privateers.
I first learned about letters of marque and reprisal in researching my great-great-great-great-grandfather Captain William H. Dobbs of New York, who was nearly hung for piracy in Boston in 1756, but was instead given letters of marque by the British and encouraged to harrass the French during the French and Indian War. He gladly did so, and captured at least one French frigate near Haiti.
In the news coverage of the Vietnamese Prime Minister visiting Microsoft last week, it was noted that software used in Vietnam was estimated to be 92% pirated, the highest rate of piracy in the world. It seems to me that countries such as Vietnam and China that have no intellectual property laws (or lax enforcement thereof) are effectively issuing letters of marque and reprisal to all their citizens who pirate software or entertainment content. Though trade reprisals and actions against private foreign actors are generally ill-advised for both sides, there would certainly be poetic justice in the US authorizing some privateers to go out and seize ships full of Vietnamese and Chinese goods.