Pennsylvania Governor Josh Shapiro said on Tuesday he could not support Nippon Steel's $15bn acquisition of US Steel (X.US), because the United Steelworkers Union was opposed to the merger.
Mr Shapiro's comments are important as he is a running mate of Vice-President Kamala Harris. The president has been opposed to the deal for months, although he has not directly called for it to be blocked.
Mr Shapiro said at a Treasury Department event attended by Treasury Secretary Janet Yellen: “As governor, from a state perspective, if the United Steelworkers are not happy with this agreement, and they are not, then I am not happy with this agreement.”
He added: “If I don’t see a future for the US steel industry in Pennsylvania, and it’s worse than it is now, I’m going to be unhappy, so I’m really worried.”
Nippon Steel and US Steel withdrew their application to the US foreign investment committee last week and plan to resubmit it before the US election. The companies aim to have the 45-day review period of the US foreign investment committee overlap with the political transition.
Former president Donald Trump said in January he would block the deal but has been silent since, while his running mate, JD Vance, has criticised the deal.
Last month, Democratic senator Sherrod Brown of Ohio and two other Democratic senators wrote to the Biden administration urging it to issue an executive order to block the deal.
Nippon Steel has promised to protect jobs, factories and pensions, but union leaders say they fear the Japanese company is making those promises to win public support.