The US justice department is looking into claims that lobbyists have tried to use bribes to secure a presidential pardon, unsealed court papers show.
They say that in August investigators began investigating a “secret lobbying scheme” possibly involving attempts to contact White House officials.
The redacted filings do not give any names, but the justice department says no government official is being probed.
In a tweet, President Trump referred to the investigation as “fake news”.
It is common for outgoing presidents to use their right to issue pardons, which wipe out convictions.
President Trump – who is due to leave office in January, although he is still contesting his election defeat in the courts – has used the procedure a number of times.
Last week he pardoned his former national security adviser Michael Flynn, who pleaded guilty to lying to the FBI.
Meanwhile, US media say Mr Trump has been discussing the possibility of pardoning family members.