President Biden is using his final days in office to block a controversial sale of U.S. Steel to a Japanese company, making good on his opposition to the proposed purchase by a foreign buyer.

In an announcement released Friday, the outgoing president, who has less than three more weeks in office, said he was blocking the proposed $14 billion takeover from Nippon Steel of Japan because of the potential threat to national security.

“It is my solemn responsibility as president to ensure that, now and long into the future, America has a strong domestically owned and operated steel industry that can continue to power our national sources of strength at home and abroad,” Mr. Biden said. “And it is a fulfillment of that responsibility to block foreign ownership of this vital American company.”

President-elect Trump had also opposed the sale to Nippon Steel, vowing during his campaign and more recently that he would kill the deal.

“I am totally against the once great and powerful U.S. Steel being bought by a foreign company, in this case Nippon Steel of Japan. Through a series of Tax Incentives and Tariffs, we will make U.S. Steel Strong and Great Again, and it will happen FAST,” Trump said in a post on Truth Social last month.

“As President, I will block this deal from happening. Buyer Beware!!!”

Mr. Biden also announced that he was increasing tariffs on steel imports to protect a robust domestic industry, claiming that more than 100 new steel and iron mills have opened during his time in the White House.

“For too long, U.S. steel companies have faced unfair trade practices as foreign companies have dumped steel on global markets at artificially low prices, leading to job losses and factory closures in America,” he said. “I have taken decisive action to level the playing field for American steelworkers and steel producers by tripling tariffs on steel imports from China.”

Mr. Biden’s decision comes after a December report from the Committee on Foreign Investment in the United States, in which the panel said it could not reach a consensus on the potential risk of Nippon Steel purchasing U.S. Steel, leaving the decision to the White House.

In its final evaluation, however, they warned that the purchase could reduce the output of domestic steel production, pose “risks to the national security of the United States,” and even deal a blow to the transportation and energy sectors.

“Potential reduced output by U.S. Steel could lead to supply shortages and delays that could affect industries critical to national security.”

Mr. Biden killed the deal despite advice from senior advisers, who warned that rejecting the deal could damage relations with Japan, according to the Washington Post.

Both Nippon and U.S. Steel have recently said they would pursue legal action against the government for what they claim were improper procedures while considering the sale.

While some steelworkers, particularly at western Pennsylvania, supported the deal saying that it would keep jobs in the region, union leaders were opposed.

“[Our] only priority has been the long-term viability of their facilities and our domestic steel industry,” the United Steelworkers Union president, David McCall, previously said. “Nippon is a serial trade cheater and U.S. Steel is viable as a standalone company.”