WASHINGTON (Dow Jones)--A World Trade Organization appeals panel agreed Thursday with an earlier finding that the U.S. failed to stop using a method of calculating antidumping duties called "zeroing."

The Geneva-based organization didn't rule completely in favor of the European Union in its long-running dispute against the U.S. But it upheld most of the findings made by a WTO panel in December, including that the U.S. didn't comply with an earlier ruling adopted by the institution's dispute-settlement body against the use of zeroing in calculating antidumping duties.

The U.S. and E.U. had appealed parts of the December ruling.

"To the extent that the United States has failed to comply with recommendations and rulings of the [dispute-settlement body] in the original proceedings, they remain operative," the appeals panel said.

It recommended that the dispute-settlement body ask the U.S. to "implement fully the recommendations and rulings" of the ruling against zeroing.

The E.U. and other countries have long complained about the U.S. practice of zeroing, in which exported goods that are sold at a higher price than in the home market are excluded when calculating antidumping duties. The E.U. argues that the method exaggerates the extent of dumping, which occurs when a country exports goods at a price below what they cost at home.

The appeals panel also upheld findings that the U.S. didn't comply within a reasonable period of time the WTO's ruling against using zeroing in antidumping duties against imports of steel products from Sweden and the Netherlands.

Debbie Mesloh, a spokeswoman at the U.S. Trade Representative's office, said the ruling "raises a number of troubling questions and implications," including how the findings would be put into practice.

In addition, she said the report was about compliance, and not the original WTO rulings on the use of zeroing.

"With respect to those underlying findings, as we have repeatedly said, the WTO has overreached by inventing new obligations to limit the use of antidumping measures, when such obligations were never agreed to by the WTO Members," Mesloh said in a statement. "Today's report compounds the problems with the earlier rulings."

The dispute-settlement body has 30 days to accept or reject the appeals-panel report.