Business associates of former National Security Advisor Michael Flynn were issued grand jury subpoenas by federal prosecutors who are investigating Russian interference in the 2016 presidential election, according to reports.

Prosecutors are seeking records and documents that might shed light on Flynn’s business dealings in the period after 2014, when he stepped down from his role as director of the Defense Intelligence Agency under the Obama administration.

The news came just hours after the president fired FBI Director James Comey, who confirmed last week a wide-ranging investigation into Trump-Russia ties is ongoing under the joint authority of the Justice Department’s National Security Division and the Attorney’s Office, which issued the subpoenas in Alexandria, Virginia.

After Trump nominated Flynn, the retired general failed to formally disclose payments and work he had performed for the Russian state-sponsored news agency RT, a $45,000 speaking fee, and his $500,000 consultation contract with Turkey’s government in his SF-86 security clearance application—a federal offense.

Flynn was forced to resign by the president after it was revealed that he had misled vice president Mike Pence and other administration officials about conversations he’d had with Russian Ambassador Sergey Kislyak, in which he allegedly discussed the lifting of U.S. sanctions on Russia.

The House Oversight Committee, staging its own investigation into the Trump campaign’s associations with Russian officials, published classified documents in a redacted form that prove Flynn was made aware of the illegality of taking unapproved foreign payments as a former military officer.

The committee also requested the White House documentation related to the Trump administration’s vetting of Flynn but, so far, the White House has refused to release those documents.

According to CNN, Flynn’s lawyer, the Alexandria Attorney’s Office, the Justice Department and the FBI declined to comment on the latest revelations.