Sept 25 (Reuters) - U.S. Steel (X.N) said on Wednesday the board of arbitration has ruled in favor of Nippon Steel's (5401.T), opens new tab $14.9 billion buyout of the company, but the United Steelworkers union disagreed with the decision.

The board, jointly selected by the company and the union to settle disputes, ruled that U.S. Steel had satisfied each of the conditions of the successorship clause of its basic labor agreement with the USW.

"The arbitrators accepted at face-value Nippon Steel's statement that it would assume the Basic Labor Agreement," USW said.

The union said the decision did not change its opposition to the deal.

Japan-based Nippon Steel did not immediately respond to a request for comment.

The deal has faced political opposition since it was signed last December. Democratic presidential candidate Kamala Harris and her Republican challenger Donald Trump have supported U.S. Steel remaining American owned.

Nippon Steel had paid a hefty premium to clinch the deal for U.S. Steel on bets it could benefit from U.S. President Joe Biden's infrastructure spending bill.

Earlier this month, U.S. Steel warned that a failure to conclude the deal would put thousands of U.S. union jobs at risk and signaled that it would close some steel mills and potentially move its headquarters out of the politically important state of Pennsylvania.