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.

Nippon Steel and U.S. Steel are filing a federal lawsuit challenging the Biden administration’s decision to block a proposed nearly $15 billion deal for Nippon to acquire Pittsburgh-based U.S. Steel

A first lawsuit was filed in the U.S. Court of Appeals for the District of Columbia Circuit, “challenging violation of the Constitutional guarantee of due process and statutory procedural requirements,” the companies said in a joint statement.