U.S. Steel said on Wednesday the board of arbitration, jointly selected by the steelmaker and the United Steelworkers union to settle disputes between them, has ruled in favor of Nippon Steel's $14.9 billion buyout deal.

The arbitration board ruled that U.S. Steel has satisfied each of the conditions of the successorship clause of its basic labor agreement with the USW, the company said.

Nippon Steel had clinched the deal to buy U.S. Steel last December over rivals, including Cleveland-Cliffs, ArcelorMittal and Nucor, paying a hefty premium as it bet the steelmaker would benefit from U.S. President Joe Biden's infrastructure spending bill.

The deal, however, has faced political oppositions, including from Democrat presidential candidate Kamala Harris and her Republican challenger Donald Trump ahead of the elections in November.