U.S. Treasury Secretary Janet Yellen said on Wednesday that Nippon Steel's planned acquisition of U.S. Steel received a "thorough analysis" by an interagency review body that was sent to President Joe Biden,

The suit, filed in the U.S. Court of Appeals for the District of Columbia, alleges that it was a political decision and violated the companies’ due process.

U.S. Steel and Japan’s Nippon Steel sued the United States government on Monday in a last-ditch attempt to revive their attempted merger after President Biden blocked it last week on the basis that the transaction posed a threat to national security.

Nippon Steel is poised to expand its operations in the U.S. and India as it hunts for growth and protection from cheap Chinese exports after its bid for U.S. Steel was blocked by the White House, analysts say.

The onetime dynamo is fighting to revive a takeover by Nippon Steel. Other tie-ups could also face obstacles, and going it alone could force cutbacks.