The U.S. Justice Department said presidents from 1867 to the present have appointed federal judges while Congress was not in session.
The Bush administration is defending Bill Pryor's appointment to the Eleventh U.S. Circuit Court of Appeals, which has been challenged by Sen. Edward Kennedy of Massachusetts.
Kennedy said the appointment amounts to an end-run on the Senate's right to confirm or reject the president's choices for judgeships.
Pryor was appointed during the President's Day recess in February 2004 after his nomination stalled in the Senate.
But Kennedy said allowing an appointment during a short break could open the door for appointments being made on weekends.