A Japanese steelmaker seeking to acquire U.S. Steel said Wednesday that U.S. citizens would make up the majority of the board of directors, as the $15 billion proposal faces mounting political opposition ahead of the U.S. election in November.

In a statement detailing governance plans, Nippon Steel said three of the board’s independent directors would be U.S. citizens, as would “core senior management members.”

In the face of resistance from the United Steelworkers union, President Joe Biden and the two major candidates running to succeed him, Nippon Steel — Japan’s largest steelmaker — has argued that the acquisition would benefit both companies and their employees as well as the United States and Japan, a key U.S. ally.

“Nippon Steel continues to believe that the transaction will enhance American national security by reinforcing U.S. Steel and its domestic production capabilities, bringing cutting-edge technologies into the United States, and ultimately making the American industrial base and supply-chain more resilient and better positioned to compete against future pressures from state-supported Chinese competitors,” the company said in a statement.

Vice President Kamala Harris, the Democratic presidential nominee, came out against the deal for the first time Monday at a joint rally with Biden in the critical swing state of Pennsylvania.

“It is vital for our nation to maintain strong American steel companies,” Harris said to applause in Pittsburgh, where U.S. Steel is based. “And I couldn’t agree more with President Biden, U.S. Steel should remain American-owned and American-operated.”

The United Steelworkers union, which says the sale could have major implications for workers, supply chains and U.S. national security, welcomed Harris’ opposition to it, saying she “once again made it clear that she will always stand up for steelworkers.”

Former President Donald Trump, the Republican presidential nominee, last month reiterated a promise in February to block the deal if elected. Biden first expressed opposition to the purchase in March.

In a statement on Monday, U.S. Steel said it remained “committed to the transaction with Nippon Steel, which is the best deal for our employees, shareholders, communities and customers.”

Nippon Steel said Wednesday that it would prioritize production at U.S. Steel to meet demand in the American market, and that the company headquarters would remain in Pittsburgh. 

It said U.S. citizens would make up an internal officer-level “trade committee” that will make recommendations to the U.S. Steel board on trade matters and document the decision-making process, and that decisions on trade matters would require approval by a majority of the independent American directors “to ensure that such decisions are made without interference by Nippon Steel.”

The company also previously said there would be no layoffs or plant closures as a result of the deal, which was announced last December.

The governance policy announced Wednesday is designed “to ensure the benefits of the transaction, while also maintaining U.S. Steel as an iconic American company,” Nippon Steel said.