The ruling sets the stage for the imposition of preliminary duties and prompts fears on the Canadian side of the border that jobs would be affected. The Trade Commission announced its determination in early January, saying Canadian lumber is "allegedly subsidized and sold in the United States at less than fair value."
The preliminary finding could force U.S. importers of Canadian lumber to pay cash deposits to cover preliminary countervailing duties early next month. Softwood producers in Canada worry the move would lead to plant closures and job losses.
Canada exported about $4.7 billion worth of lumber to the U.S. last year, according to the U.S. Commerce Department.
President Donald Trump has made trade a key issue, promising during the campaign to renegotiate the North American Free Trade Agreement and kill the Trans-Pacific Partnership.