The companies said today in a joint statement that they filed a lawsuit in the US Court of Appeals for the District of Columbia Circuit challenging Biden’s decision and what they say is the failure of the Committee on Foreign Investment in the US panel to consider the deal on national security grounds.

They also filed a suit in the US District Court for the Western District of Pennsylvania against rival US steelmaker Cleveland-Cliffs Inc, Cliffs’ CEO Lourenco Goncalves, and US Steelworkers union President David McCall.

“Both Nippon Steel and US Steel have engaged in good faith with all parties to underscore how the Transaction will enhance, not threaten, US national security,” the companies said in the statement.

“Today’s legal actions demonstrate Nippon Steel’s and US Steel’s continued commitment to completing the Transaction,” the companies said.

US Steel shares rose 4% as of 7.25am in pre-market trading in New York.