U.S. Steel shares tumbled more than 17% on Wednesday as the White House is reportedly preparing to block the company's planned sale to Japan's Nippon Steel.

People familiar with the matter told The Washington Post that President Joe Biden was preparing to announce that he will block the $14.9 billion deal. U.S. Steel shares have fallen 41% this year.

Vice President Kamala Harris, the Democratic presidential nominee, said U.S. Steel "should remain American-owned and American-operated" during a campaign event in Pittsburgh Monday. Former President Donald Trump, the Republican nominee, is also opposed to the deal.

U.S. Steel CEO David Burritt told The Wall Street Journal on Wednesday that the company would likely be forced to close plants and move its headquarters from Pittsburgh if the deal is blocked. Burritt told the Journal that the transaction is crucial to keeping U.S. Steel's older plants competitive and maintaining jobs.

The deal has been under review by the Committee on Foreign Investment, a body that scrutinizes the potential impact of foreign investment in the U.S. on national security. U.S. Steel has not received any update or executive order related to the committee's review, a company spokesperson said.

"We continue to stand by the fact that there are no national security issues associated with this transaction, as Japan is one of our most staunch allies," the U.S. Steel spokesperson said.

"We fully expect to pursue all possible options under the law to ensure this transaction, which is best future for Pennsylvania, American steelmaking, and all of our stakeholders, closes," the spokesperson said.

The bipartisan opposition to U.S. Steel's acquisition by Nippon demonstrates a rising tide of protectionism in the U.S. even toward a company that is based in a close ally such as Japan.

U.S. Steel has 20 million metric tons of annual production capacity. Nippon, headquartered in Tokyo, is Japan's largest steelmaker. The companies combined would have up to 86 million tons of capacity.

A Nippon Steel spokesperson said the acquisition would revitalize the American Rust Belt and benefit U.S. national security "in a way no alternative can."

"Simply put, U. S. Steel and the entire American steel industry will be on much stronger footing because of Nippon Steel's investment in U. S. Steel – an investment that Nippon Steel is the only willing and able party to do so," the spokesperson said.