US President Joe Biden has blocked the $14.1 billion sale of United States Steel to Nippon Steel, halting a deal that has sparked a political firestorm and tensions between the United States and Japan.

Biden made his formal decision on Friday after the case was referred to him by a US security review board, ahead of a deadline early next week.

“We need great American companies that represent the major share of American steelmaking capacity to continue leading the fight on behalf of American national interests,” Biden said in a written statement from the White House.

He said the takeover would have put one of the country’s largest steel producers under foreign control and created “a risk to our national security and our vital supply chains.”

“US Steel will remain a proud American company — American-owned, American-run, by American workers — the best in the world,” the president said in a statement.

The companies have indicated they may challenge the legal basis for any ban, raising the possibility that the matter could remain in dispute. President-elect Donald Trump has also vowed to block the deal.