Territorial premiers are making the case in Washington that Northern Canada is key to continental security, diplomacy and economic opportunity as Canadian leaders continue their diplomatic push against threatened U.S. tariffs.

It is the first time all 13 premiers have travelled to the American capital together.

U.S. President Donald Trump's planned 25 per cent tariffs on steel and aluminum imports would be stacked on top of other levies on Canadian goods, says a White House official who confirmed the plan Tuesday on background.

Canadian premiers are taking up the Team Canada mantle in Washington this week for a joint mission to convince U.S. President Donald Trump to drop tariff threats for good.

Donald Trump has signed executive orders to slap 25 per cent tariffs on all steel and aluminum imports into the United States, including Canadian products, starting March 4 — the same deadline given to Canada to convince the U.S. president to halt his plan for across-the-board duties.

Energy and Natural Resources Minister Jonathan Wilkinson, Industry Minister François-Philippe Champagne and Defence Minister Bill Blair are in the U.S. capital this week making the case that Canada should not be dragged into a trade war.

Trudeau held a news conference Saturday evening to announce that Canada will respond with an immediate $30-billion retaliation package, which will be followed by $125 billion in duties on American products in 21 days to give companies and supply chains time to find alternatives.

The president says there is nothing that Canada, Mexico or China can do to prevent the tariffs from being implemented.

U.S. President Donald Trump says he will decide Thursday night whether to include oil in his tariff plan, as he confirmed his intention to impose devastating duties on Canadian imports on Saturday.

Trump also told the crowd that Canada has been tough to deal with over the years.