WASHINGTON--President Joe Biden came out in opposition to the planned sale of U.S. Steel to Nippon Steel of Japan, saying on Thursday that the U.S. needs to “maintain strong American steel companies powered by American steel workers.”

In a statement, Biden added: “U.S. Steel has been an iconic American steel company for more than a century, and it is vital for it to remain an American steel company that is domestically owned and operated.”

By opposing the merger, Biden has chosen to support unionized workers in a critical election year at the risk of upsetting the business community and an essential ally in Japan. Thursday’s announcement, coming as Biden is campaigning in the Midwest, could have ripples in his race against the presumptive Republican presidential nominee, Donald Trump.

The Democratic president has made the restoration of American manufacturing a cornerstone of his agenda as he seeks reelection, and he has the endorsements of the AFL-CIO and several other prominent unions. The White House said Thursday that Biden called David McCall, president of United Steelworkers, to reiterate his support for its members.

Nippon Steel announced in December that it planned to buy the Pittsburgh-based steel producer for $14.1 billion in cash, raising concerns about what the transaction could mean for unionized workers, supply chains and U.S. national security.

The Japanese company reiterated Friday how the deal benefits U. S. Steel, union workers, the American steel industry and national security.

“Nippon Steel will advance American priorities by driving greater quality and competitiveness for customers in the critical industries that rely on American steel while strengthening American supply chains and economic defenses against China,” it said in a statement out of Tokyo.

“No other U.S. steel company on its own can meet this challenge while also meeting antitrust requirements,” it said, stressing it already employs 4,000 American workers.

The company has also committed to keeping the U.S. Steel name and Pittsburgh headquarters.

The company, which is the world’s fourth largest steel producer, launched a website with supportive statements from Larry Summers, the former treasury secretary, and Pat Toomey, a Republican and former senator from Pennsylvania.

Shortly after the steel deal was announced, the White House indicated it would be under review by the secretive Committee on Foreign Investment in the United States. The government does not officially provide updates on the CFIUS review process.

Biden has a big megaphone to weigh in on the matter, but he is not intervening in the review process or formally blocking the deal, according to a person familiar with deliberations who insisted on anonymity to discuss the situation.

When asked about the deal on Thursday, White House national security spokesman John Kirby declined to say if the president wanted to stop it outright or would be amendable to changes in its structure. But Kirby told reporters that the United States sees its alliance with Japan as “stronger than it’s ever been.”

Still, the president holds sway over CFIUS. The treasury secretary leads the committee, which is also composed of the heads of federal agencies and, as deemed appropriate, directors of White House councils on the economy and national security.

Trump said earlier this year after meeting with the Teamsters union that he would stop the U.S. Steel acquisition: “I would block it. I think it’s a horrible thing, when Japan buys U.S. Steel. I would block it instantaneously.”

Biden traveled Thursday to Saginaw, Michigan, which was once home to multiple General Motors plants and where he hopes his backing from union workers can resonate with voters.

The city is in a swing county that narrowly backed Trump in 2016 and then flipped to Biden in 2020, making it a crucial contest in this year’s presidential race.

Biden has a close relationship with the United Steelworkers. He gave the union members “personal assurances” that he has their backs, according to a February statement by the union about Nippon Steel’s plans. U.S. Steel is headquartered in Pennsylvania, another key state in this year’s election.

The United Steelworkers issued a statement last week after meeting with representatives from Nippon Steel that it had concerns about whether the company would honor existing labor agreements and about the company’s financial transparency, adding that there were “barriers” to closing a merger.

The U.S. considers Japan to be one of its closest allies and a key partner in countering China’s ambitions and influence in Asia. Biden has visited the country twice as president and will host Japanese Prime Minister Fumio Kishida at the White House on April 10.

But Nippon Steel’s connections to China have raised concerns within the Biden administration. More than half the steel produced globally comes from China, according to the World Steel Association. India is the second-largest producer, followed by Japan and the United States.

The U.S. Chamber of Commerce warned in a February blog post that it would be foolhardy of the Biden administration to block the deal. Doing so could hurt foreign investment into the United States, cause other countries to block the overseas investments that U.S. companies want to make and undermine the U.S.-Japan alliance, the chamber said.

John Murphy, the head of international issues for the chamber, said Thursday that it was “inappropriate and counterproductive” of Biden to politicize the CFIUS review.

“It’s imperative that the CFIUS review proceed; and if, as expected, it reveals no national security concerns, the sale should proceed,” Murphy said.

But Sen. Bob Casey, D-Pennsylvania, who is up for reelection, applauded Biden’s statement, saying, “I’ll work like hell against any deal that leaves our Steelworkers behind.”