The panel investigating the alleged interference by Russia in the US election has issued a subpoena to Trump's former security adviser Michael Flynn.
The Senate Intelligence Committee issued the demand for documents from Flynn relating to Russia's alleged meddling.
In a joint statement from the committee's chairman Richard Burr and vice chairman Mark Warner said they issued the legal demand after Flynn was asked to produce the documents on 28 April but his lawyer did not hand them over.
On May 8 the former acting US attorney general Sally Yates said she warned President Trump's administration in January that Mr Flynn "could be blackmailed" by Russian officials.
Mr Flynn, a retired general who advised Donald's Trump's election campaign, was sacked in February after it emerged he concealed the nature of his contact with Russia's US ambassador, Sergei Kislyak, ahead of Trump's inauguration.
He emerged as a central figure into possible collusion between Trump's campaign and Russia, and was accused of relaying misleading information to vice president Mike Pence.
Ms Yates, who was originally appointed by the Obama administration, told a Senate Judiciary subcommittee that she felt Pence "was entitled to know" he was relaying incorrect information about Flynn to the American public.
Mr Flynn was a former aid to Barack Obama but was sacked as head of the Defence Intelligence Agency in 2014.
Russia and the Trump administration deny any part in colluding on the US election.