(Reuters) - The union representing employees of United States Steel ( X ) on Tuesday said it would not support Japanese firm Nippon Steel's ( NISTF ) draft agreement to gain support for its takeover of the U.S. company.

In December, Nippon agreed to buy U.S. Steel for roughly $15 billion but the deal faces an uphill battle to approval amid bipartisan opposition in a U.S. election year.

The United Steelworkers (USW) union said that it received a letter along with a draft agreement from Nippon Steel ( NISTF ) on March 27.

The USW said that while Nippon has made several commitments, including not laying off employees through Sept. 1, 2026 and defending U.S. Steel against unfair foreign trade, the letter "does not provide a meaningful basis for a resolution of the ongoing dispute."

The March 27 proposal ignores a previous letter sent by the USW about the specific actions that Nippon would be required to take to gain its support, the USW added.

The union added that it is open to meeting with Nippon Steel ( NISTF ) officials to discuss the status of the transaction in the coming weeks.