President Donald Trump’s fired national security adviser is refusing to hand over files to a Senate panel probing alleged Russian political meddling.
According to US media, Michael Flynn will invoke his constitutional right against self-incrimination.
The Senate Intelligence Committee is investigating possible links between the Trump campaign and Kremlin.
Mr Flynn stood down in February after it emerged he lied about his contacts with the Russian ambassador.
The Senate committee issued a subpoena – a legal summons – two weeks ago to obtain his documents.
The panel, another congressional committee and the FBI are investigating claims that Russian hackers tried to help Mr Trump win last November’s presidential election, and whether members of his campaign colluded with the alleged Kremlin conspiracy. Mr Flynn’s name has cropped up repeatedly in the matter.
Lawyers for him reportedly cite an “escalating public frenzy against him” for his unwillingness to co-operate, according to a letter obtained by the Associated Press news agency.
His attorneys argue that “any testimony he provides could be used against him”.
My Flynn’s legal representative has previously demanded immunity from “unfair prosecution” before his client co-operates with the committee.
The former Army lieutenant general is expected to invoke the fifth amendment to the US constitution, which protects Americans from being legally compelled to testify against themselves in a criminal case.
Republican Senator James Lankford, who serves on the Senate Intelligence Committee, tweeted: “It is Mike Flynn’s right to plead the 5th.
“We will get to the truth one way or another.
“We need facts, not speculation & anonymous sources.”
Last week the committee’s chairman Senator Richard Burr told reporters that Mr Flynn was “not co-operating” with the investigation.
Shortly after Mr Flynn left the White House, the Department of Defense also launched an investigation when it emerged he had received payments for a speech in Russia and for lobbying on Turkey’s behalf.
Former acting Attorney General Sally Yates testified to senators earlier this month that she had warned the White House 18 days before Mr Flynn was fired that he was vulnerable to Russian blackmail.
The Kremlin had “leverage” over the ex-national security adviser, Ms Yates testified.
Mr Flynn misled the White House about discussing US sanctions against Russia with Moscow’s envoy, Sergei Kislyak, before Mr Trump took office.
Mr Trump injected a fresh impetus into the Senate investigation after he himself met the Russian ambassador and foreign minister in the White House earlier this month.
The US president said in that encounter that he had just fired the FBI director because he was a “real nut job” and his dismissal eased “a great pressure because of Russia”, the New York Times reported.
During the Oval Office chat, which US media were not invited to cover, Mr Trump also reportedly divulged secret information on the military campaign against so-called Islamic State.
Israel was reportedly the source of that sensitive intelligence.
But while in Jerusalem on Monday, Mr Trump told reporters repeatedly that he “never mentioned the word Israel” in his meeting with Russian officials.
Former FBI director Robert Mueller was appointed last week as special counsel to lead the FBI investigation following Mr Trump’s firing of the law enforcement agency’s director, James Comey.
Attorney General Jeff Sessions has been forced to recuse himself from that inquiry after he neglected to tell senators during his confirmation hearings about his own meeting with Mr Kislyak.
If Mr Flynn continues to refuse to comply with Senate investigators, it is thought they could vote to hold him in contempt of Congress, or even refer his case for possible criminal charges.