Nippon Steel is on track to finalize its planned $15 billion acquisition of U.S. Steel by the end of September as it steps up talks with key stakeholders, particularly labor unions, an executive said on Wednesday.

The deal by the world's No.4 steelmaker to buy U.S. Steel has drawn criticism from some Democratic and Republican U.S. lawmakers and the powerful United Steelworkers (USW) union.

Former U.S. President Donald Trump, whose protectionist "America First" policies were a hallmark of his term in office, has said he would "instantaneously" block the deal if he won the Nov. 5 election.