The US faces $21m (£10.6m) in annual trade sanctions as a result of its online betting ban, the World Trade Organization has ruled.
Antigua and Barbuda was awarded the right to impose sanctions that target US services, copyrights and trademarks.
Laws passed in the US in October 2006 effectively made it illegal for foreign internet gaming firms to trade there.
But in March the trade body delivered a final ruling saying that the US online betting ban was illegal.
Last year the US stopped US banks and credit card companies from processing payments to online gambling businesses outside the country, effectively killing off the market for overseas gambling firms.
About half of the world's online gamblers are based in the US, and the market is estimated to be worth $15.5bn.
The WTO ruling said the US was breaking trade law by targeting online gambling firms, without equal application of the rules to US firms offering online betting on horse and dog racing.
Earlier this week, the EU said the US would offer its member countries trade concessions as compensation for its refusal to lift internet gambling laws.
Granted, $21 million is practically a drop in the bucket to the U.S., and it remains to be seen whether they'll actually pay up. Still, it's nice to remind the United States that they can't do whatever the fuck they want. And it's nice for the rank hypocrisy and two-faced nature of these laws (banning on-line gambling because it's "bad" but keeping lotteries and allowing bets on dog- and horse-racing) to be pointed out at this level.