The failed acquisition of US Steel by Nippon Steel for $15 billion escalates into a legal dispute. The two steel companies filed two lawsuits on Monday after President Joe Biden blocked the deal due to "credible evidence" of security concerns.

The first lawsuit demands the annulment of Biden's decision due to "unlawful political interference." The second is directed against Cleveland-Cliffs, its CEO Lourenco Goncalves, and the president of the United Steelworkers (USW), David McCall. It accuses the defendants of "illegal and coordinated actions to prevent the transaction.

These lawsuits demonstrate our ongoing commitment to complete the transaction," declared Nippon Steel and US Steel in a statement.

President-elect Donald Trump, who will take office in two weeks, spoke out against a takeover of US Steel on Monday. On his platform Truth Social, he wrote that US Steel would benefit as an independent company from the planned tariff regime.

Why sell when tariffs will make US Steel a much more profitable company?" asked Trump and added, "US Steel could take the lead again.

Biden's veto has strained relations between Washington and Tokyo and raised doubts about the USA's openness to foreign investments. The Committee on Foreign Investment in the United States (Cfius) had previously not reached a consensus on a potential national security threat posed by the deal.

Nippon Steel promised extensive investments of 2.7 billion dollars for modernization and guaranteed not to reduce production capacity at most locations for at least ten years. Nevertheless, Biden refused approval.

Japanese Prime Minister Shigeru Ishiba sharply criticized the actions of the USA. "The blockade sends a worrying signal to potential Japanese investors," he said on Monday. "We urge the US government to address these concerns.