Nippon Steel Chief Executive Eiji Hashimoto says the top Japanese steelmaker is standing firm on its proposed acquisition and poses no security risks.

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.

The companies also filed a second suit against the head of the United Steelworkers union and steel company Cleveland Cliffs, claiming the two worked together to block the U.S. Steel and Nippon deal. Download the FREE WPXI News app for breaking news alerts.

The suit, filed 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.

Nippon Steel, whose multibillion-dollar proposal to buy struggling US Steel was blocked by President Joe Biden last week, says it is considering taking legal action against the US government.

President Biden’s block of a $14 billion sale of Pittsburgh-based US Steel to Japan’s Nippon Steel has caused significant backlash from Republicans. “Joe Biden, frankly, I’m not sure he knows the difference between Japan and China,

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President-elect Trump has also opposed Nippon Steel's $15 billion acquisition of U.S. Steel, which President Biden blocked last week.

Mr. Biden says he blocked the $14 billion takeover of U.S. Steel by Japan's Nippon Steel on the grounds the sale was a threat to national security.