WASHINGTON -- Donald Trump has made clear his intention to lower the protectionist hammer. He announced plans Thursday to invoke a rarely-used legal provision allowing tariffs for matters of national security.

He says he wants tariffs of 25 per cent on steel, and 10 per cent on aluminum. It's unclear if there will be any exception for Canada -- the No. 1 U.S. supplier of both products. Trump says he'll sign an executive order next week.

The news hit like a thunderclap -- affecting the stock market and the Canadian dollar and prompting worldwide threats of retaliation. It also drew considerable pushback in Washington.

Some key quotes:

-- "Twenty-five per cent for steel. It will be 10 per cent for aluminum. And it will be for a long period of time... So we'll probably see you sometime next week. We'll be signing it in. And you will have protection for the first time in a long while, and you're going to regrow your industries. That's all I'm asking. You have to regrow your industries." Trump, announcing tariff plans during a meeting with industry representatives.

-- "As a key NORAD and NATO ally, and as the number one customer of American steel, Canada would view any trade restrictions on Canadian steel and aluminum as absolutely unacceptable. Any restrictions would harm workers, the industry and manufacturers on both sides of the border... It is entirely inappropriate to view any trade with Canada as a national security threat to the United States ... Should restrictions be imposed on Canadian steel and aluminum products, Canada will take responsive measures to defend its trade interests and workers." Foreign Affairs Minister Chrystia Freeland.

-- "If it happens (and there's always an if with this president), this is the most consequential protectionist action by the U.S. since Nixon's 10% across-the-board tariffs in 1971. And those didn't last very long." Edward Alden of the U.S. Council on Foreign Relations, in a tweet.

-- "We strongly regret this step, which appears to represent a blatant intervention to protect U.S. domestic industry and not to be based on any national security justification ... We will not sit idly ... The EU will react firmly and commensurately to defend our interests." European Commission chief executive Jean-Claude Juncker.

-- "This action will cause aluminum prices to rise. It is likely to lead to job losses across the beer industry." Beer-maker MillerCoors.

-- "We are not protectionists. We want a level playing field ... The trans-shipments (of Chinese steel) that go on ... we call it the whack-a-mole game. It's time for whack-a-mole to end. It's time for some fairness here. It's past time." Dave Burritt, CEO of U.S. Steel Corporation, expressing support for tariffs.

-- "Blanket tariffs that sweep in fairly traded products can backfire. They can actually hurt American jobs and workers ... I think we're all urging the president, 'Look, continue to narrow this ... Exempt those that are fairly traded.' ... You don't want to set off a trade war." Kevin Brady, Republican head of the House of Representatives committee overseeing trade.

-- "I am very concerned ... Any suggestion that Ontario-made steel or aluminum constitutes a 'national security threat' to the U.S. is false ... I am asking my federal colleagues to continue to aggressively explore all options." Ontario Premier Kathleen Wynne.

-- "There is no standard operating practice with this administration. Every day is a new adventure for us." Senior Republican Sen. John Thune, on the chaotic decision-making process that led to the announcement.

-- "I commend ΓåòrealDonaldTrump for announcing his intent to take action to protect our steelworkers from countries, like China, that cheat on trade ... For years, foreign countries have been dumping steel into our markets and costing our workers their jobs and suppressing their wages." Tweets from Bob Casey, a Pennsylvania Democratic senator.

-- "The U.S. domestic (steel) supply is relatively inelastic in the short term and costly to ramp up in the long term. That makes the first target of U.S. tariffs on these imports the U.S. customer that is stuck paying them. The trickle effect to parts and cars that cross (the) border in the buildup process means we all get punished with higher costs." Flavio Volpe of the Canadian Automotive Parts Association.

-- "China fired the first shots in this 'trade war' more than a decade ago when Beijing added more steel production capacity than it could possibly use. The flood of imports devastated our steel industry and distorted the global market. No one did a thing. Until now." -- Tweet from Scott Paul of the Alliance for American Manufacturing.

-- "Where exactly (this) leads is anyone's guess, but it is certain to be a place less stable, less predictable, and less co-operative than the place we are right now ... (It's) a Pandora's box." Trade analyst Dan Ikenson, writing for Forbes.