The subpoena, which was issued in November, also asks Giuliani to provide testimony, said the person, who declined to be identified as they were not authorised to speak publicly on the matter.

The nature of the inquiry by the US attorney in Washington DC, which began before Special Counsel Jack Smith was appointed to oversee investigations into Trump, remains largely under wraps.

The former mayor, who has served as Trump’s personal attorney, did not respond to requests by Reuters for comment.

A spokesman for the US Attorney for the District of Columbia did not immediately respond to a request for comment.

The source said the subpoena sought, among other things, copies of any retainer agreements between Trump and Giuliani, or the Trump campaign and Giuliani, and records of payments and who made those payments.

In December, a District of Columbia attorney ethics committee said Giuliani violated at least one attorney ethics rule in his work on a failed lawsuit by Trump challenging the 2020 election results. Giuliani’s New York state law license was suspended in June 2021 after a state appeals court found he had made “demonstrably false and misleading” statements that widespread voter fraud undermined the 2020 election won by his Democratic opponent, Joe Biden.