The Japanese firm’s planned purchase of its U.S. rival was blocked last week by U.S. President Joe Biden after a year of diplomatic tension, political debate and lobbying efforts from the companies and unions. Biden, who had previously said he opposed the tie-up, cited national-security risks, despite Japan being a close ally. 

The companies have filed a petition with the federal appeals court in Washington, arguing that the Committee on Foreign Investment in the United States failed to consider the deal on national-security grounds, and that Biden’s order to block it was made for “purely political reasons.” They also filed a lawsuit against rival Cleveland-Cliffs Inc. and United Steelworkers President David McCall, alleging anticompetitive activities.

“There is no reason—or need—to give up on this deal,” Eiji Hashimoto, chairman and chief executive officer of the Japanese steelmaker, told reporters, adding Nippon Steel and U.S. Steel were focused on pushing ahead with the current agreement. “I have no thoughts of alternative plans.”

The two companies are asking the U.S. Court of Appeals for the District of Columbia Circuit to set aside an “unlawful” review and Biden’s subsequent order, and to demand a new review, they said in a joint statement.

“There will be truths revealed through the lawsuit, like the fact that the review violated the law,” Hashimoto said at a press conference in Tokyo. “By revealing that the review was not conducted with national security in mind, we believe there is a chance for us to win the lawsuit.”

A months-long court battle is now likely, but it is not clear that will improve the prospects for the deal to ultimately succeed—U.S. law gives the president the power to kill any merger deemed a threat to national security. President-elect Donald Trump, meanwhile, has also voiced his opposition to the takeover.

The deal did create a split within Biden’s administration, though. Secretary of State Antony Blinken, currently on a visit to Japan for farewell talks with Prime Minister Shigeru Ishiba, was among those who pitched an option to allow the deal with conditions. Proponents argued the block was an affront to a close ally, and undercut Biden’s efforts to reinvigorate alliances and create friendly supply chains.

Hashimoto said the U.S. market was “the most promising” among developed nations and “essential” for the company’s strategy—but Nippon Steel would continue to look at other growth markets, including India and Southeast Asia. 

Nippon Steel’s deal to buy U.S. Steel included a $565 million break fee for the American company. Hashimoto said that the penalty fee only comes into play if the merger contract breaks. That has not happened, he added.