Former White House chief strategist Steve Bannon has been ordered to give testimony to a grand jury in the investigation into Russian election meddling.
The order came shortly after Mr Bannon refused to answer questions on the same topic before a separate panel where he was issued with another subpoena.
His reluctance to answer the questions put to him by the House Intelligence Committee has led to accusations of him being "gagged" by the US president as the investigation - led by special counsel Robert Mueller - continues into Donald Trump's election campaign's links to Russia.
Mr Bannon will became the highest-ranking person who served in the Trump White House to be called before a grand jury as part of the special counsel's investigation, The New York Times reported.
Democrat Adam Schiff of California said: "This was effectively a gag order by the White House."
A spokeswoman for Mr Bannon did not respond to media requests for comment on Tuesday afternoon.
White House press secretary Sarah Huckabee Sanders dismissed the Democrats' concerns, saying "no one" had encouraged Mr Bannon not to be transparent during questioning but there's a "process of what that looks like".
"As with all congressional inquiries touching upon the White House, Congress must consult with the White House prior to obtaining confidential material. This is part of a judicially recognised process that goes back decades," Ms Sanders told reporters.
A White House official said the president did not seek to formally exert executive privilege over Mr Bannon - a move that would have barred him from answering certain questions.