U.S. Steel shares fell more than 15% after report White House seeks to block Nippon Steel’s takeover of Japan.

The drop comes after Democratic presidential candidate Kamala Harris this week echoed President Joe Biden’s concerns about the $15 billion deal, saying U.S. Steel “should remain American-owned and operated.”

People familiar with the matter told The Washington Post that President Joe Biden is preparing to announce that he will block the $14.9 billion deal.

For its part, Nippon Steel said that U.S. citizens will make up a majority of U.S. Steel’s board of directors, which will also include three independent directors who will also be U.S. citizens. The Japanese company said that key members of its senior management will also be U.S. citizens.

The chief executive of US Steel said the company would close steel mills and possibly move its headquarters out of Pittsburgh, Pennsylvania, if a plan to sell it to Japan’s Nippon Steel collapses. Nippon Steel has pledged to invest about $3 billion in the company’s old Pittsburgh plants, the Financial Times reported, citing chief executive David Burritt, who said the move was crucial to maintaining the company’s competitiveness and preserving jobs.