The first hearing for the lawsuit over former US President Joe Biden's block of the US Steel buyout by Nippon Steel begins on Monday.

The buyout plan was first examined by the Committee on Foreign Investment in the United States, or CFIUS, but it failed to reach a consensus, sending the matter to Biden. The former president issued an order to block the takeover on January 3, citing national security concerns.

In response, the Japanese and US steelmakers filed the lawsuit with a federal appeals court in Washington. Documents they submitted will be examined at Monday's hearing.

The companies say there was unlawful political influence. They demand Biden's order be overturned and CFIUS conduct a fresh review.

They say the former president publicly announced his plan to block the deal in March 2024 before CFIUS even began its formal review, in order to "curry favor" with the leadership of the United Steelworkers union in his bid for reelection.