The U.S. Senate Intelligence Committee on May 10 subpoenaed former Trump national security adviser Michael Flynn, demanding documents related to its investigation into Russia's election meddling.
Committee Chairman Richard Burr and Vice Chairman Mark Warner said the panel had first requested the documents from Flynn on April 28, but Flynn's lawyer declined to cooperate.
It was the committee's first subpoena in the Russian investigation.
Flynn was fired by Trump in February after less than a month on the job. The White House said he misled Vice President Mike Pence and other top officials about his communications with Russia's ambassador to the United States.
Flynn has become a major focus of several congressional investigations into Russia and the election.
Former Acting U.S. Attorney General Sally Yates testified this week that she had warned the White House that Flynn had been compromised by his contacts with Russia and could have been vulnerable to blackmail.
The subpoena was announced a day after Trump abruptly fired FBI Director James Comey, who had been leading the bureau's investigation of Russia and the election.
Burr is one of several prominent Republicans who have expressed strong doubts about the timing of Trump's action.