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Dissidents are seeking to oust Mr. Fain as president of the United Automobile Workers union as he prepares to run for re-election next year.

By Neal E. Boudette

Two years ago, Shawn Fain led the United Automobile Workers union through simultaneous strikes at three large carmakers, a strategy that helped produce big gains in wages and benefits for the union’s members.

Mr. Fain was hailed by progressives and Democratic politicians like former President Joesph R. Biden Jr. who saw him as the vanguard of a new generation of labor leaders who could get more workers to sign up to join unions, reversing the long slide in the labor movement’s ranks. He campaigned for Mr. Biden and later former Vice President Kamala Harris and exchanged insults with President Trump.