Feb 5 (Reuters) - United Steelworkers President David

McCall filed a motion to dismiss U.S. Steel and Nippon

Steel's ( NISTF ) lawsuit against him, the union said on

Wednesday.

The two steelmakers filed the lawsuit in January after then

U.S. President Joe Biden blocked a $14.9 billion bid for the

123-year-old American steelmaker by the Japanese firm.

It named McCall, rival bidder Cleveland-Cliffs ( CLF ) and

its CEO Lourenco Goncalves, citing "their illegal and

coordinated actions" aimed at preventing the deal to allow

Cliffs to monopolize key steel markets.

"U.S. Steel and Nippon launched a frivolous and

unsubstantiated attack on our union simply for exercising our

First Amendment rights," the union said in a statement, arguing

that it was both the union's "right" and "responsibility" to

speak out against mergers that hurt union members and national

security.

Nippon Steel ( NISTF ) declined to comment. U.S. Steel said in a

statement that it would respond to the motion to dismiss shortly

and would continue to pursue its claim. "There are no valid

legal defenses to that illegal conduct," it added.

Biden blocked the deal on national security grounds but

delayed enforcement pending a separate suit from the companies.

The proposed tie-up had become highly politicized ahead of

November's U.S. presidential election, with both Biden and

Donald Trump vowing to terminate it.

The USW opposed the deal on grounds of lack of transparency

and job security risks, despite Nippon's multiple attempts at

assuaging its concerns.

The union has, however, shown its support for Cliffs, which

was reported to be partnering with peer Nucor ( NUE ) to prepare

a potential all-cash bid for U.S. Steel last month.

Cleveland-Cliffs ( CLF ) also filed a motion on Tuesday to dismiss

the lawsuit against the company and Goncalves.

McCall filed the motion in the Western District of

Pennsylvania.