U.S. tariffs on steel and aluminum imports doubled Wednesday, as President Donald Trump continued to ratchet up levies on foreign metals that he claims will help revitalize American steel mills and aluminum smelters.

The White House called the increased tariffs, which rose to 50% from 25% just after midnight Eastern time, a matter of addressing “trade practices that undermine national security.” They were announced during Trump’s visit to a mill run by U.S. Steel last week, and appear to be aimed at currying favor with steelworkers and the steel industry, including those in swing states like Pennsylvania, where U.S. Steel is based.

The higher levies have already rankled close allies that sell metal to the United States, including Canada, Mexico and Europe. They have also sent alarms to automakers, plane manufacturers, homebuilders, oil drillers and other companies that rely on buying metals.

In an executive order, Trump said the higher tariffs would “more effectively counter foreign countries that continue to offload low-priced, excess steel and aluminum in the United States market and thereby undercut the competitiveness of the United States steel and aluminum industries.”

Kevin Dempsey, the president of the American Iron and Steel Institute, an industry group, praised the move. He said China and other countries oversupplied the international market, making it harder for U.S. producers to compete.

“Given these challenging international conditions that show no signs of improvement, this tariff action will help prevent new surges in imports that would injure American steel producers and their workers,” Dempsey said.

But companies that use steel and aluminum to make their products criticized the tariffs, saying they would add costs for American consumers.

Robert Budway, the president of the Can Manufacturers Institute, said doubling the steel tariff would further increase the cost of canned goods at the grocery store.

“This cost is levied upon millions of American families relying on canned foods picked and packed by U.S. farmers and can makers,” he said.

The increase Wednesday is the latest in a mounting array of import taxes Trump has announced since returning to the Oval Office in January, including the 25% tariff on steel and aluminum in March. Taken together, the president’s trade tactics have increased concerns of a global downturn and heightened corporate America’s worries about the cost of doing business.

Economists have pointed out that tariffs on factory inputs such as metals risk slowing U.S. manufacturing, since they raise prices for factories.

An economic analysis published by the U.S. International Trade Commission, an independent, bipartisan government agency, suggested that while the steel and aluminum tariffs levied in Trump’s first term helped American steel and aluminum producers, they hurt the broader economy by raising prices for many other industries, including automaking.

The Aluminium Association of Canada said in a statement Tuesday that the expanded tariff “makes Canadian exports to the U.S. economically unviable” and that “the industry may be forced to diversify trade toward the European Union.”