"That has only been done once before and is, I believe, a very potent weapon," said Mark Mendel, a lawyer representing Antigua, after the ruling. "I hope that the United States government will now see the wisdom in reaching some accommodation with Antigua over this dispute."

Though Antigua is best known for its pristine beaches and tourist attractions, the dozens of online casinos now based there are vital to the island's economy, serving as its second-largest employer.

By pressing its claim, trade lawyers said, Antigua could set a precedent for other countries to sue the United States for unfair trade practices, potentially opening the door to electronic piracy and other dubious practices around the world.

Still, implementation will prove difficult, the lawyers say.

"Even if Antigua goes ahead with an act of piracy or the refusal to allow the registration of a trademark, the question still remains of how much that act is worth," said Brendan McGivern, a trade lawyer with White & Case in Geneva. "The Antiguans could say that's worth $50,000, and then the U.S. might say that's worth $5 million - and I can tell you that the U.S. is going to dog them on every step of the way."

The United States has aggressively fought Antigua's claims at every step.

A WTO panel first ruled against the United States in 2004, and its appellate body upheld that decision one year later. In April 2005, the trade body gave the United States one year to comply with its ruling, but that deadline passed with little more than a statement from Washington that it had reviewed its laws and decided it has been in compliance all along.