Supreme Court Justice Clarence Thomas temporarily stopped a subpoena for testimony from Lindsey Graham, a Republican senator from South Carolina.
Attorneys for Graham asked Thomas to delay the senator's appearance before the grand jury, which is investigating possible criminal interference in Georgia's presidential election in 2020.
On Thursday, a panel of judges on the 11th Circuit U.S. Court of Appeals unanimously rejected Graham's request to temporarily block the subpoena.
Graham didn't show that he was likely to succeed on the appeal challenging the legality of the demand for his testimony. The grand jury's subpoena was upheld by a federal judge last month.
The actions of Trump and his allies, including Graham, who contacted state election officials and others on the heels of the election, which was won by President Joe Biden, are being investigated by a grand jury.
Trump pressured state officials to take actions that could have changed the outcome of the election, as part of a similar effort in other swing states. The Georgia Secretary of State was urged by Trump to find enough votes to wipe out Biden's win.
Thomas did not refer the question to the Supreme Court when he issued the hold on the subpoena.
The subpoena would be delayed pending further orders from the Supreme Court. Thomas told Fulton County prosecutors to respond to Graham's request for a stay of the subpoena by Thursday, two days before he issued the stay.
Lawyers for Graham and the prosecutor will have more time to argue if the subpoena should be allowed to stand.
Donald McGahn did not reply to the request.
The spokesman for the Fulton County District Attorney wouldn't say if prosecutors would respond to Graham's application on Thursday.
The speech and debate clause of the U.S. constitution protects members of Congress from legal risk if they make comments about legislative business.
He made a call to the Georgia Secretary of State after the election.
According to the 11th Circuit panel's ruling last week, a federal district court judge had ordered that a Fulton County prosecutor couldn't question Graham about certain parts of the call.
There is disagreement about whether his phone calls with Georgia election officials were legislative investigations.