Canadian Prime Minister Justin Trudeau says Canada and the U.S. could suffer from a "thickening" border a day after the Trump administration imposed new tariffs on softwood lumber and trade tensions between the two countries escalated.

Trudeau responded Tuesday to news that the U.S. plans to impose a 20-percent tariff on softwood lumber entering the United States from Canada.

Canada's Liberal Party leader says the two countries are economically interconnected, but it's not a one-way relationship. He says millions of U.S. jobs depend on smooth flow of goods, services and people back and forth across the border.

The U.S. and Canada typically enjoy a friendly trading relationship, but things have soured in recent months as the two countries and Mexico prepare to renegotiate the North American Free Trade Agreement.