U.S. Steel chief executive said the company would close steel mills if its planned sale to Nippon Steel collapses, as the Biden administration is moving closer to blocking the deal. CEO David Burritt said the nearly $3 billion that Japan-based Nippon Steel has pledged to invest in the Pittsburgh company’s older mills is critical to keeping them competitive and maintaining workers’ jobs. “We wouldn’t do that if the deal falls through,” Burritt said in an interview.