The top-ranked Democrat in Washington has called President Donald Trump's alleged tax avoidance a question of "national security", APA reports citing BBC.
Nancy Pelosi, Speaker of the House of Representatives, asked whether Mr Trump owed money to foreign interests, following an article on his financial records by the New York Times.
It alleges Mr Trump paid only $750 (£580) in federal income tax in both 2016 and 2017.
Mr Trump called the report "fake news".
Speaking on NBC, Ms Pelosi said the report showed that "this president appears to have over $400m in debt".
"To whom? Different countries? What is the leverage they have?" she asked, adding: "So for me, this is a national security question."
"The fact that you could have a sitting president who owes hundreds of millions of dollars that he's personally guaranteed to lenders, and we don't know who these lenders are," she said, and suggested that Mr Trump may be indebted to Russian President Vladimir Putin.