United States Steel is disputing the United Steelworkers’ allegations that the steelmaker breached its labor agreement with the union by failing to provide information about critical developments of the company’s sale to Nippon Steel.

The Pittsburgh-based manufacturer said it repeatedly reached out to the USW during the company’s strategic review before the sale, but says it couldn’t share more information because the union chose not to sign a nondisclosure agreement.

U.S. Steel’s agreement to sell itself to the Japanese steel-maker has turned into a political football, with key politicians and opponents of the deal seizing on the union’s claims that U.S. Steel didn’t comply with the labor agreement.