A spokesperson for the inspector general, an independent watchdog, confirmed the request and declined further comment. The request was previously reported by CNBC.

The Fed has been renovating two of its office buildings in Washington for several years at a current cost estimate of about $2.5 billion, $700 million more than originally expected. Trump administration officials have seized on the expense and some alleged amenities in the remodeled buildings to extend their criticism of Powell, whom the president has attacked for not reducing the Fed’s short-term rate.

On Thursday, Russ Vought, the president’s top budget advisor, said that President Donald Trump is “extremely troubled” about the “ostentatious overhaul” and suggested that it may be violating local building rules.

The letter represented a sharp escalation in the Trump administration’s efforts to gain greater control over the Fed, an independent agency charged with seeking stable prices and maximum employment. Independence from day-to-day politics has long been seen as a critical element in the Fed’s ability to achieve those goals.

Trump has repeatedly demanded that Powell cut the short-term interest rate that the central bank controls, in part because the president believes it will lower the government’s borrowing costs.

Trump and some of his officials have encouraged Powell to resign, though there is no indication he will leave before his term ends next May.