Peter Mandelson has been asked to testify to the US Congress over his relationship with the paedophile financier Jeffrey Epstein.
A letter from two Democrat members of the House of Representatives called on the former British ambassador to Washington DC to answer questions from the House Oversight Committee as part of their probe into Epstein.
Mr Mandelson's links with Epstein have led to calls for Keir Starmer to stand down as Prime Minister.
Critics have questioned the Prime Minister's judgment in appointing the peer as US ambassador, which is considered the most prestigious posting in British diplomacy.
The letter to Lord Mandelson, signed by representatives Robert Garcia and Suhas Subramanyam, said: "While you no longer serve as British Ambassador to the United States and have stepped down from the House of Lords, it is clear that you possessed extensive social and business ties to Jeffrey Epstein and hold critical information pertaining to our investigation of Epstein's operations.
"Given the appalling allegations regarding Epstein's conduct, we request that you make yourself available for a transcribed interview with Committee staff regarding the crimes of Jeffrey Epstein and his co-conspirators."
Mr Mandelson's representatives have been contacted for comment.
