U.S. Steel shares plummet amid questions over the fate of its merger with Nippon Steel

U.S. Steel shares plunged on Wednesday as Wall Street questioned whether its $14.1 billion deal with Japan's Nippon Steel is at risk of derailing.

Shares of U.S. Steel plunged as much as 25% in afternoon trading after the Washington Post reported President Joe Biden is preparing to formally block the proposed acquisition. As of 2:35 p.m., shares of U.S. Steel were down $7.12, or 20%, to $28.48. 

At an afternoon briefing, a White House official downplayed the Washington Post report, which cited three people familiar with the president's plans. In a statement, the White House cited a process of review by the Committee on Foreign Investments in the United States, or CFIUS, a panel chaired by the Treasury Secretary.