Canada is taking its softwood lumber case to the World Trade Organization.

The Canadian government today requested WTO consultations with the U.S. over American lumber duties.

It called the duties unfair, unwarranted and deeply troubling.

The U.S. has imposed a series of penalties, arguing that Canada unfairly subsidizes its lumber companies through cheap access to public land.

It's the latest instalment in an off-again, off-again dispute, as efforts to renew a deal that expired in 2015 have proven unsuccessful; American companies have refused to sign off on a new Canada-U.S. accord.

Canada is also fighting the case through NAFTA's dispute-resolution system.