In its 64-page report, the panel found that the duties the United States imposed in February 2005 because of alleged price dumping by Ecuadorean exporters were inflated because of Washington's use of a practice known as "zeroing" to calculate whether the shrimp were being sold at below-cost price.
According to previous panel decisions, zeroing leads to inflated margins of dumping, and thus higher duties.
The case, which was not contested by Washington, is now likely to go to the WTO's dispute settlement arm, which could request the United States bring its antidumping measures into line with global trade rules.
U.S. trade officials were not immediately available for comment.
The United States also imposes antidumping duties on shrimp imports from Brazil, China, India, Thailand and Vietnam.
Source: Forbes
WTO rules against US on shrimp
US - U.S. antidumping duties on shrimp imports from Ecuador break international trade rules, a World Trade Organization panel said Tuesday.