(Reuters) - United Steelworkers president David McCall filed a motion to dismiss a lawsuit filed against him by U.S. Steel and Nippon Steel ( NISTF ), the union said on Wednesday.

The two steelmakers filed a lawsuit against McCall, rival bidder Cleveland-Cliffs ( CLF ), its CEO Lourenco Goncalves last month "for their illegal and coordinated actions" aimed at preventing the $14.9 billion deal.

Former President Joe Biden had initially blocked the deal on national security grounds in January, but delayed its enforcement until June.

U.S. Steel's takeover by Japan's Nippon Steel ( NISTF ) had become highly politicized ahead of the U.S. Presidential election in November, with both Biden and Donald Trump vowing to terminate it.

The deal also underwent a lengthy antitrust review by the Committee on Foreign Investment in the United States (CFIUS) under Biden's Presidency.

The companies also alleged Biden of unlawfully blocking the deal in another lawsuit filed against his administration.

The deal, which was blocked on national security concerns, had always faced opposition from the USW on grounds of lack of transparency and job security risks, despite Nippon's multiple attempts at assuaging their concerns.

The USW, however, has shown its support for Cliffs, which was also reported to partner with peer Nucor to prepare a potential all-cash bid for U.S. Steel last month.

U.S. Steel and Nippon have alleged Cliffs, Goncalves and McCall of colluding to allow Cliffs to "monopolize the domestic steel markets" by thwarting any other attempts to buy the 123-year-old American steelmaker.

McCall filed the motion in the Western District of Pennsylvania, with USW calling U.S. Steel and Nippon's lawsuit a "frivolous and unsubstantiated attack" on the union for exercising its first amendment rights.