Geneva, Switzerland (Jan. 25, 3:50 p.m. ET) -- A World Trade Organization panel has told U.S. trade authorities that they need to amend anti-dumping duties placed on polyethylene retail carrier bags imported from Thailand.

The Geneva-based WTO said the U.S. Commerce department, in calculating the duties to be placed on bags made in Thailand, used a controversial practice called “zeroing.” With the tactic, authorities considering whether a product is being dumped at a price below its manufacturing cost ignore cases where the product costs more in the United States than in the home country.

U.S. trade officials did not oppose the action brought by the Thai government at the WTO, which means a change in policy is likely.

This latest ruling, which was released Jan. 22, applies to an anti-dumping complaint that the United States had first filed in 2003. The U.S. International Trade Commission issued its anti-dumping duty order in August 2004.

In the WTO panel’s proceedings, Thailand had alleged the practice of zeroing created artificial margins of dumping “where none would otherwise have been found or, at a minimum, to inflate margins of dumping,” according to documents released in Geneva.

WTO concluded that the order used to determine the dumping margins for individually investigated Thai exporters “were not based on total facts available.”