Federal prosecutors have issued grand jury subpoenas seeking business records from people who worked with former US national security adviser Michael Flynn when he was a private citizen, CNN reported Tuesday.

Citing people familiar with the matter, CNN said the subpoenas were issued by the US Attorney’s Office in Alexandria, Virginia. They targeted people who worked with Flynn on contracts after he was pushed out of his job as director of the Defense Intelligence Agency in 2014, it reported.

Flynn later joined the Trump campaign but was fired as the White House national security adviser by President Donald Trump in February after Flynn failed to tell the truth about his contacts with the Russian ambassador to the United States.

Flynn’s attorney, Robert Kelner, did not respond immediately to a request for comment. A Justice Department spokeswoman said the department does not comment on the existence of ongoing investigations.

The Federal Bureau of Investigation is looking into allegations that Russia meddled in the 2016 presidential election to benefit Trump, as well as possible links to the Trump campaign.

Russia has repeatedly denied interfering in the US election and the Trump administration denies allegations of collusion with Russia.

Trump fired FBI Director James Comey on Tuesday, saying he had lost confidence in Comey over his handling of an election-year email scandal involving then-Democratic presidential nominee Hillary Clinton.

Flynn, a retired general, has emerged as a central figure in the Russian probes.

Investigators have been looking into whether Flynn properly disclosed payments from clients with links to foreign governments, including Russia and Turkey, CNN said.