The long trade battle over the pricing of Canadian softwood-lumber shipments to the U.S. has become more intense, after a U.S. trade panel’s Dec. 7 ruling that the exports have hurt domestic producers.

The U.S. International Trade Commission unanimously decided that Canadian shipments have “materially injured” U.S. lumber companies. The panel’s action clears the way for the Commerce Dept. to impose tariffs on the Canadian products. The Commerce Dept. on Nov. 2 set tariffs on Canadian lumber shipments as high as 23.76%.

Canada is preparing to challenge the U.S. move in international trade tribunals. Minister of Foreign Affairs Chrystia Freeland said in a statement that the U.S. anti-dumping and countervailing duties are “punitive” and “unwarranted.” She also said Canada has started challenges against the U.S. under the North American Free Trade Agreement and before the World Trade Organization.

U.S. lumber companies hailed the ITC’s decision. U.S. Lumber Coalition co-Chair Jason Brochu said in a statement, “The evidence presented to the ITC was clear—the massive subsidies that the Canadian government provides to its lumber industry and the dumping of lumber products into the U.S. market by Canadian companies cause real harm.”

The National Association of Home Builders estimated that the tariffs will add $1,360 to the price of a single-family home in the U.S.