The White House said Nippon Steel's plan to buy US Steel should be examined from a national security perspective, even though Japan is a "close ally."
A statement raised concerns about the deal's potential impact on supply chain reliability.
The $15 billion purchase of the 122-year-old steelmaker would create one of the largest steel companies in the world.
The influential United Steelworkers (USW) union also criticized the deal as "short-sighted".
Joe Biden's national economic adviser, Lyle Brainard, said the US president believes "the purchase of this iconic American company by a foreign entity - even a close ally - seems to require serious scrutiny".
Ms. Brainard added that President Biden views US Steel as a "major component" of the nation's overall steel production.
As he seeks re-election, Biden has cast himself as one of America's most pro-union presidents by joining a wave of protests by striking auto workers. "President Biden believes that union workers are the best workers in the world," the White House statement added.
The USW welcomed the White House announcement, saying the deal could "impact the future of domestic steelmaking."
"US Steel has repeatedly made it clear that its first and only priority is short-term financial gain for shareholders, even if it comes at the expense of workers," they added./BGNES