The companies accuse the president, head of steelworkers union and Cleveland-Cliffs CEO of teaming up to block the transaction.

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.

U.S. Steel and the Japanese firm that had sought to acquire it are suing the Biden administration after the president announced he was blocking a proposed deal for the iconic American manufacturer.