The Senate Intelligence Committee has issued a subpoena to former national security adviser Michael Flynn for documents related to its investigation into Russian interference in the presidential election, committee leaders announced Wednesday.

According to a brief joint statement from chair Richard Burr Richard Mauze BurrRep. Mark Walker says he's been contacted about Liberty University vacancy Overnight Defense: Trump rejects major cut to military health care | Senate report says Trump campaign's Russia contacts posed 'grave' threat Senate report describes closer ties between 2016 Trump campaign, Russia MORE (R-N.C.) and ranking member Mark Warner Mark Robert WarnerIntelligence chief says Congress will get some in-person election security briefings Overnight Defense: Trump hosts Israel, UAE, Bahrain for historic signing l Air Force reveals it secretly built and flew new fighter jet l Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' House approves bill to secure internet-connected federal devices against cyber threats MORE (D-Va.), the committee first requested the documents in an April 28 letter to Flynn, but he declined through counsel to cooperate with the request.

Flynn had previously offered to testify before the Senate and House intelligence committees — which are both investigating Russian interference in the election — in exchange for immunity, but it does not appear that either committee has accepted the offer.

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The former intelligence head was fired in February for misleading Vice President Pence and other White House officials about the contents of a December phone call with Russian ambassador Sergey Kislyak.

Flynn has also been under scrutiny for accepting payments from Russia and Turkey and allegedly misleading the government about them.

In April, the committee sent a series of requests for records from Trump associates on any dealings with Russians. As of the deadline to produce documents Tuesday afternoon, Burr told reporters that the committee had received only two responses — and hinted that he was willing to issue subpoenas to compel the rest.

One of those responses, from former Trump foreign policy advisor Carter Page, is publicly known. Burr declined to disclose the second.

Aside from Page and Flynn, informal Trump adviser Roger Stone and former foreign policy adviser Paul Manafort were also reportedly sent letters.

The letters ask for the men to list any meetings they might have had with Russian officials between June 16, 2015 — the day Trump formally launched his campaign — and Trump's inauguration on Jan. 20, as well as records of any communications during the period.

The senators also want details on any financial assets or real estate holding tied to Russia, and a broader list of meetings between any Trump campaign aides and Russians.

In December 2015, Flynn was paid $45,000 to speak at an event hosted in Moscow by the Kremlin-backed network RT, during which he was seated with Russian President Vladimir Putin. He also received payments for additional speeches to Russian firms Kaspersky and Volga Dnepr.

As a retired military officer, Flynn is prohibited under the emoluments clause of the Constitution from accepting payment from a foreign government without advance permission from both the secretary of State and the secretary of the Army.

According to documents released by House Oversight Committee ranking member Elijah Cummings (D-Md.), Flynn did not disclose the RT payment when he applied to renew his security clearance in January 2016, just a month after he traveled to Moscow.

Flynn’s lawyer has claimed that he briefed the DIA “extensively” both before and after the 2015 trip.