Stein ran against President Donald Trump as a member of the Green Party. She said in a statement Tuesday that she's complying with the committee's document request.
Stein attended a 2015 dinner sponsored by Russian media outlet RT with Russian President Vladimir Putin. She said the documents show that she "made the trip with the goal of reaching an international audience and Russian officials" with messages of Middle East peace and international cooperation against climate change.
Senate Intelligence Committee Chairman Richard Burr, R-N.C., appeared to confirm the investigation Monday. Asked what the committee wanted to know about from Stein's campaign, Burr responded: "collusion with the Russians."
Stein received about 1 percent of the popular vote in the 2016 election.
