Nippon Steel and U.S. Steel filed 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..

The suit, filed Monday 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.

“From the outset of the process, both Nippon Steel and U. S. Steel have engaged in good faith with all parties to underscore how the Transaction will enhance, not threaten, United States national security, including by revitalizing communities that rely on American steel, bolstering the American steel supply chain, and strengthening America’s domestic steel industry against the threat from China,” the companies said in a prepared statement Monday. “Nippon Steel is the only partner both willing and able to make the necessary investments.”

Nippon Steel had promised to invest $2.7 billion in U.S. Steel’s aging blast furnace operations in Gary, Indiana, and Pennsylvania’s Mon Valley. It also vowed not to reduce production capacity in the United States over the next decade without first getting U.S. government approval.