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.

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

Separate lawsuits from Nippon Steel and U.S. Steel target President Joe Biden as well as a steelworkers union head and a rival steelmaker’s CEO.

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.