US Special Counsel Robert Mueller has subpoenaed the Trump Organization for documents, including some related to Russia, the New York Times reported on Thursday, citing two people briefed on the matter.
Details of the subpoena were not available, the New York Times reported, but it was the first known time Mr Mueller demanded materials directly related to US President Donald Trump's businesses.
US stock prices fell on the report, with the S&P 500 reaching session lows, while the dollar slipped against the euro and yen and yields on US government debt moved lower.
The White House declined to comment specifically on the report and referred questions to the Trump Organization.
"We're going to continue to fully cooperate. Out of respect for the special counsel, we're not going to comment," White House spokeswoman Sarah Sanders said during a briefing on Thursday.
A Trump Organization spokeswoman did not immediately respond to a request for comment.
- Another former Trump aide talks to Russia probe
- Putin suggests 'Jews' may have meddled with US election
- Trump blames FBI's Florida failings on Russia investigation
Mr Mueller is investigating Russian attempts to influence the 2016 US election, and potential collusion by Trump aides. Russia has denied US intelligence agencies' conclusion that it meddled in the election and Mr Trump has said there was no collusion between his campaign and Moscow officials.
Mr Mueller has charged several Trump associates and more than a dozen Russians.
Peter Carr, a spokesman for Mr Mueller, declined to comment on the Times report.
Witnesses interviewed by Mr Mueller have been asked about a possible real estate deal in Moscow, although the Trump Organization has denied having any real estate holdings in Russia, the Times reported.