Senate Intelligence Committee chairman Richard Burr and ranking member Mark Warner said the step was taken after Flynn rejected their April 28 request to provide information on his contacts with Russian officials and businessmen.
"The subpoena requests documents relevant to the Committee's investigation into Russian interference with the 2016 election," Burr and Warner said in a joint statement.
President Donald Trump had sacked Flynn in February after it was revealed that he had lied about his conversations with Russian ambassador to the US, Sergey Kislyak.