US President Joe Biden says he has blocked the proposed $14.9bn (£12bn) purchase of US Steel by Japanese rival Nippon Steel.
A White House announcement of his executive order cited “credible evidence” that the firm “might take action that threatens to impair the national security of the United States”.
Biden decided to block the deal despite intense efforts to sway him in recent days by some of his senior advisors, who reportedly warned that rejecting a sizable investment from a top Japanese corporation like Nippon Steel could damage Washington’s relations with Tokyo.
BBC News has contacted Nippon Steel and US Steel for comment.
The decision was left with the outgoing President Biden after a US government panel failed to reach a consensus in late December on whether the acquisition by Nippon Steel may threaten Washington’s national security.
Biden was legally required to act within a 15-day deadline, after the deadlock by the Committee on Foreign Investment in the United States (CFIUS).
He has repeatedly criticised the deal, joining other US politicians who have called the transaction into question.
They include President-elect Donald Trump and the incoming vice-president, JD Vance.
The deal became caught up in the 2024 US presidential campaign when Pennsylvania emerged as a critical swing state and leaders of the United Steelworkers union loudly opposed it.
Nippon Steel has previously described the transaction as a lifeline to Pennsylvania’s much-diminished steel industry in the past.
The Japanese company and US Steel have also previously suggested they may pursue legal action against the government if the deal did not happen.