Nippon Steel has hired former U.S. Secretary of State Mike Pompeo to help complete a proposed purchase of United States Steel, a deal facing bipartisan opposition from Donald Trump and U.S. President Joe Biden.

Pompeo, who served as the U.S.’ top diplomat under Trump, will be an adviser to the Japanese company for its $14.1 billion purchase, according to people familiar with the matter, speaking on condition of anonymity to discuss the move. The deal’s fate is unclear as it undergoes a national security review and faces opposition by the United Steelworkers union.

Nippon Steel confirmed the move in a written statement, praising Pompeo’s record. Pompeo said the U.S. should expand its manufacturing base by partnering with allies in a statement also provided by the company.