US special counsel Robert Mueller has reportedly subpoenaed Deutsche Bank, seeking records as part of his investigation into allegations that Russia helped Donald Trump win the 2016 US presidential election.
The report in German business newspaper Handelsblatt cites only "informed circles", while a spokesman said Deutsche Bank had no comment.
Handelsblatt said it was not clear whether the demand sought information on the US president or on other members of his circle.
Deutsche Bank has been one of the few major banks willing to regularly lend to Mr Trump, who alienated large banks in New York with his past financial troubles.
Over the years, the bank’s cumulative loans to Mr Trump added up to billions, and loans originally worth $300m remain outstanding.
Handelsblatt said the subpoena was received several weeks ago.
In May, five Democratic members of the House of Representatives sent a letter to Deutsche Bank chief executive John Cryan asking the bank to turn in any records relating to Mr Trump's accounts and any ties to Russia.
The bank refused, saying it had to respect legal requirements to keep client data private.