A World Trade Organization ruling approved a long-outlawed U.S. trade policy on Tuesday, when a panel of adjudicators said Washington's use of "zeroing" to calculate anti-dumping tariffs was permissible in the case of Canadian softwood lumber.

The WTO's long-running row over zeroing is a technical dispute that turned into a power struggle between the United States and the arbiters of international trade law.

The United States has suffered a string of defeats at the WTO over zeroing, a calculation method ruled to have unfairly increased the level of U.S. anti-dumping duties. Zeroing occurs when the investigating authority ignores, by treating as zero, cases where export prices are higher than prices at home. Critics have said this artificially inflates dumping margins...

This was excerpted from the 9 April 2019 edition of CBC News.