President Donald Trump will sign off on steep tariffs on steel and aluminium imports next week, hitting producers like China.
Flanked by US metals executives at the White House, he said a 25 percent tariff would be placed on steel products, and a 10 percent tariff would be imposed on aluminium.
Mr Trump tweeted that the US was suffering from "unfair trade".
The US imports four times more steel than it exports, and is reliant on steel from more than 100 nations.
In Thursday's announcement, Mr Trump promised to rebuild the American steel and aluminium industries, which he said had suffered "disgraceful" treatment from other countries for decades.
"And when it comes to a time when our country can't make aluminium and steel - and somebody said it before and I will tell you - you almost don't have much of a country, because without steel and aluminium your country is not the same.
"We need great steel makers, great aluminium makers for defence."
Citing China, Mr Trump said "we haven't been treated fairly by other countries".
He spoke as Chinese economic adviser Liu He, a friend of Chinese President Xi Jinping, visited the White House.
Mr Liu was due to meet separately with one of the US president's top economic advisers, Gary Cohn.
Throughout his presidential campaign and since taking office, Mr Trump said cheap imports from China were harming the viability of US industry.
China isn't the only country to export steel to the US - 110 countries and territories do so. And China is only the 11th biggest exporter to the US - Canada, Brazil, South Korea, Mexico and Russia are the five biggest.
Last year, the president ordered an investigation by Secretary of Commerce Wilbur Ross into "whether steel imports threaten to impair the national security", drawing a link between economic prosperity and the country's security.
Mr Ross' report was published last month. It said US national security was indeed threatened, and made three recommendations, one of which was putting in place a 24% tariff on all steel imports.
It also proposed adding a 7.7 percent tariff to all aluminium imports, among other options.
On Thursday morning, President Trump tweeted: "Our Steel and Aluminum industries (and many others) have been decimated by decades of unfair trade and bad policy with countries from around the world.
"We must not let our country, companies and workers be taken advantage of any longer. We want free, fair and SMART TRADE!"
During his campaign, he said that foreign countries were "dumping vast amounts of steel all over the United States, which essentially is killing our steelworkers and steel companies".