The U.S. trade representative is taking issue with the latest decision from the World Trade Organization on Canada’s long-standing dispute with its largest trading partner over exports of softwood lumber.

Robert Lighthizer says the panel report from the W.T.O., which rejects the bulk of the U.S. complaint, unfairly protects Canada from American retaliation against what he calls “massive” lumber subsidies north of the border.

Lighthizer also says the report proves U.S. claims that the trade body’s oft-maligned dispute resolution system is unfair and biased against American interests.

The latest report stems from Canada taking issue with U.S. efforts to impose duties on softwood exports in 2017, although the cross-border dispute over lumber has been raging between the two countries for nearly 40 years.

U.S. producers have long argued that Canada’s system of regulating so-called stumpage fees through the provinces results in the unfair subsidization of an industry that is privately owned and operated south of the border, where pricing is set by the competitive marketplace.

As a result, the U.S. argues that imports of Canadian lumber are eligible for countervailing duties, according to American trade law.