TOKYO (Reuters) -Nippon Steel Vice Chairman Takahiro Mori said on Tuesday the Japanese company remains committed to talks with the United Steelworkers (USW) labour union over its bid to acquire U.S. Steel.

Mori, the key negotiator of the $14.9 billion buyout deal, said USW President David McCall "has not seriously considered any of the proposals that we have presented" in a letter to the U.S. Steel employees.

"We just need USW leadership to come to the table. I am hopeful they will do so in the very near future," Mori wrote.

The USW did not immediately reply to a Reuters request for a comment.

The deal has faced opposition from high-profile Democrats and Republicans ahead of the U.S. November presidential elections, including from Democrat candidate Kamala Harris and her Republican competitor Donald Trump.

Sources told Reuters last week the U.S. national security panel reviewing the deal let the companies refile their application for approval, delaying a decision on the politically sensitive merger until after the Nov. 5 presidential election.

In the letter, Mori said Nippon Steel was committed to maintaining U.S. Steel's blast furnace operations for the long term and that it will not use slabs made overseas instead of slabs made in USW-represented U.S. Steel facilities.

The Japanese company will honour all U.S. Steel's commitments related to the union's agreements, including in labour, pension and insurance, Mori said, adding that his company will not interfere with U.S. Steel's decisions on trade matters.

The companies plan to close the deal by the end of December, pending regulatory approvals.

(Reporting by Kaori Kaneko, Kantaro Komiya and Katya Golubkova; Editing by Jacqueline Wong and Lincoln Feast.)