Senior US lawmakers have called on President Donald Trump to turn over any recordings of conversations with fired FBI director James Comey.
Senate Democratic leader Charles Schumer warned that destroying any tapes would break the law.
Republican Senator Lindsey Graham said the White House needed to "clear the air" about whether tapes existed.
The comments come after Mr Trump tweeted what appeared to be a thinly veiled threat to the former FBI chief.
He warned Mr Comey last week against talking to the media, saying he had "better hope there are no tapes" of their conversations.
The White House has neither confirmed nor denied the existence of any tapes.
Mr Schumer also warned that Senate Democrats might refuse to vote on a new FBI director until a special prosecutor is named to investigate alleged Russian meddling in the US election.
The FBI is investigating the allegations and possible ties between Moscow and the Trump campaign.
Mr Trump denies any such links and says Mr Comey had assured him he was not being investigated. He says he fired Mr Comey because he was not doing a good job.
Democrats, however, have accused President Trump of firing Mr Comey to try to thwart the FBI inquiry.
Mr Schumer told CNN that if any tapes existed "the president should turn them over immediately. To destroy them would be a violation of law".
"If there are no tapes, he should apologise to both Jim Comey and the American people for misleading them," he added.
Senator Graham told NBC that Mr Trump's tweet was "inappropriate" and called on the president to "back off and let the investigation go forward".
"You can't be cute about tapes," he said. "If there are any tapes of this conversation, they need to be turned over."
Meanwhile, President Trump has said he could announce a replacement for Mr Comey later this week.
Eleven people are reportedly being considered for the position, which requires confirmation in the Senate, and interviews began on Saturday.
Those under consideration include acting FBI Director Andrew McCabe, New York Appeals Court Judge Michael Garcia, Republican Senator John Cornyn and senior lawyer Alice Fisher.