A pair of Washington, D.C., lobbying firms reportedly received subpoenas from attorneys representing Robert Mueller, the special counsel in the Russia probe.

The subpoenas asked Mercury Public Affairs and SGR LLC for answers and records pertaining to Michael Flynn, President Trump's former national security advisor, and Paul Manafort, former Trump campaign chairman, according to the Washington Post.

SGR LLC confirmed to the Post that it received a subpoena several months ago, but Mercury Public Affairs did not confirm it received any subpoena.

Flynn was fired by Trump for lying to Vice President Mike Pence about the nature of his conversations with former Russian Ambassador to the United States Sergey Kislyak during the presidential transition. He's since become a central figure in the investigation and previously asked for immunity in order to testify about his experiences in the Trump campaign and administration.

Manafort has also become a top target in the probe. He's discussed his role in the campaign with multiple congressional committees and the FBI conducted a raid on his home in July for documents related to his business dealings with Russia and Ukrainian politicians.

Manafort was Trump's campaign chairman until beign fired over controversial payments he took while working in Ukraine.