The companies argued in a lawsuit announced on Monday that Biden violated the Constitution by blocking the merger via a sham national security review that deprived the companies of their right to a fair 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.

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.