U.S. stocks slid Thursday after President Trump Donald John TrumpBiden leads Trump by 36 points nationally among Latinos: poll Trump dismisses climate change role in fires, says Newsom needs to manage forest better Jimmy Kimmel hits Trump for rallies while hosting Emmy Awards MORE announced new, steep tariffs on steel and aluminum to be imposed next week.

The Dow Jones industrial average lost 420 points on the day, a 1.7 percent decline, while the Nasdaq and Standard & Poor's 500 indexes closed down roughly 1.3 percent each.

Trump said Thursday he would announce a 25 percent tariff on imported steel and a 10 percent tariff on aluminum from all countries that send metals to the U.S. The move is expected to lead to retaliation by trade partners.

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Reports had surfaced last week that Trump was considering such tariffs.

The Dow fell as much as 580 points following the announcement shortly after 2 p.m. The Nasdaq and the S&P also fell roughly 1.8 percent each.

The tariffs are part of an effort by the Trump administration to bolster the U.S. steel and aluminum industries, which Trump pledged to revive on the campaign trail. But the announcement tanked shares of car companies and airplane manufacturers that would spend much more on raw materials under the tariffs.

"We'll be signing it next week. And you'll have protection for a long time in a while,” Trump said, a promise he made while meeting with 15 steel and aluminum industry executives. “You'll have to regrow your industries, that's all I'm asking.”

The Commerce Department previously recommended tariffs of 24 percent on steel and 10 percent on aluminum among other potential policy changes.

Trump’s decision came against the pleas of Republican lawmakers, who argued that American consumers will bear the brunt of the cost.

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Senate Democrats up for reelection this year in states Trump won in 2016 have praised the president's plan as a way to protect American workers.

Trump has until the end of April to finalize his decision.

Updated at 4:06 p.m.