(CNN) The House Intelligence Committee is accusing former White House national security adviser Michael Flynn of failing to comply with its subpoena as part of its Russia investigation.

The committee is now demanding that Flynn appear on September 25 and provide documents by September 18, according to a letter Chairman Adam Schiff, a Democrat from California, sent to Flynn on Friday.

Flynn pleaded guilty to lying to the FBI in former special counsel Robert Mueller's investigation back in 2017, but he is still awaiting sentencing. Flynn had long been a cooperating witness for the government since his guilty plea, but earlier this year Flynn obtained a new legal team and has accused federal prosecutors of withholding significant documents and audio recordings related to his criminal charge and the Mueller investigation.

The committee says that Flynn's cooperation with the government should extend to cooperating with Congress, but he has not done so.

"General Flynn and his counsel have failed to cooperate with the Committee in all respects — he has provided no documents in response to our subpoena, nor has he engaged with the Committee in an appropriate or satisfactory manner," a committee staffer said. "General Flynn agreed to cooperate with the United States government, which should include the Congress. And while we cannot evaluate whether he has met his obligation to the Justice Department, there is no question that he has thus far failed to cooperate with the Congress in any meaningful way."

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