Steve Bannon, ex-chief strategist to US President Donald Trump, has refused to answer a broad range of questions at a committee hearing probing alleged links between the Trump campaign and Russia.
Mr Bannon had been called to testify in front of the House Intelligence Committee about his time working for Mr Trump.
He was questioned behind closed doors on Tuesday in a 10-hour meeting.
A Democrat on the committee believes he was under a White House “gag order”.
Representative Adam Schiff said that Mr Bannon’s lawyer had cited “executive privilege” – which allows the president to keep information from the public.
“Steve Bannon and his attorney asserted a remarkably broad definition of executive privilege,” Jim Himes, a Democratic member of the committee, told CNN.
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The committee issued a subpoena for him to return for a second round. His first appearance was voluntary.
Mr Bannon’s representatives have made no comment.
Asked if the White House had told him not to answer certain questions, White House spokeswoman Sarah Sanders said: “No-one has encouraged him to be anything but transparent.”
She said Congress had to consult with the White House prior to obtaining confidential material.
Republican member Mike Conaway told the press that Mr Bannon was “not an executive”, and the committee was “going to resolve the issues to get the answers”.
Earlier on Tuesday, it was reported that Mr Bannon had been issued with another subpoena, this time from former FBI director Robert Mueller, who is leading the inquiry into alleged Russian collusion during the 2016 election campaign.
