U.S. Steel (X) shares are falling 7% in premarket trading Tuesday after President-elect Donald Trump said that he would block Nippon Steel’s planned $14 billion acquisition of its American rival.

In a post on his Truth Social platform, Trump wrote he was “totally against” the takeover of the company by a foreign firm, reiterating his previous opposition to the bid. The Japanese company had agreed to buy U.S. Steel last year, but has faced pushback from the Biden administration, which extended the foreign security review period for the deal.

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

Both Trump and the White House have argued the deal would hurt U.S. workers.

CEO Has Said US Steel Would Have To Close Plants if Deal Falls Through

However, U.S. Steel Chief Executive Officer (CEO) David Burritt has said that without the promised $3 billion promised by Nippon Steel if the deal passes, the company would have to close plants and move out of its headquarters in Pittsburgh.

Neither U.S. Steel nor Nippon Steel immediately returned Investopedia requests for comment.

U.S. Steel shares are down more than 15% this year through Monday.