WASHINGTON (Reuters) - The U.S. House of Representatives’ Intelligence Committee has issued subpoenas against former White House adviser Michael Flynn and President Donald Trump’s former deputy campaign chairman Rick Gates, the panel said in a statement on Thursday.

Former national security adviser Michael Flynn exits a vehicle as he arrives for his sentencing hearing at U.S. District Court in Washington, U.S., December 18, 2018. REUTERS/Jonathan Ernst - RC1F833B3930

In a letter accompanying the subpoena, the panel’s Democratic chairman, Adam Schiff, demanded that Flynn and Gates, who have both pleaded guilty to charges related to Special Counsel Robert Mueller’s Russia investigation, provide documents by June 26 and to testify before the committee on July 10.

The committee, which is investigating Russian interference in the 2016 U.S. presidential election, said it had issued the subpoenas after Flynn and Gates declined to cooperate fully with Congress.

The move adds a new layer to a battle between the White House and congressional Democrats, who control the House of Representatives.

House Democrats are pursuing several congressional investigations of the Trump campaign, the White House and Trump’s businesses. But the White House has vowed to stonewall all of the congressional investigations and has ignored official congressional demands and requests for testimony.

On Wednesday, Trump asserted executive privilege over documents related to his administration’s push to add a citizenship question to the census.

Traditionally, presidents have cited executive privilege to block other branches of government from obtaining certain internal information from the White House.

Later that day, a House committee voted to hold two Trump administration officials in contempt for defying congressional subpoenas.

The Trump administration has also asserted executive privilege to prevent lawmakers from obtaining the unredacted Mueller report.

Mueller’s investigation ended earlier this year, with Mueller saying there was not enough evidence to conclude the Trump campaign had conspired with Russia during the election. He declined to decide whether Trump had obstructed justice.

Both Flynn and Gates pleaded guilty to charges stemming from Mueller’s probe and initially cooperated with federal prosecutors. Flynn appears to have recently changed his legal strategy, firing his lawyers and hiring a new attorney who has been critical of Mueller’s investigation.

On Thursday, Trump praised Flynn and his new lawyer on Twitter, saying: “General Michael Flynn, the 33 year war hero who has served with distinction, has not retained a good lawyer, he has retained a GREAT LAWYER, Sidney Powell. Best Wishes and Good Luck to them both!”

Powell’s office declined to comment. Gates’ lawyer did not immediately respond to a request for comment.