US Steel and Nippon, whose $14.3 billion merger was blocked by President Joe Biden last week, filed a lawsuit against the US government Monday, claiming Biden’s executive order to bar the companies from combining was signed for “purely political reasons.

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.

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.