The purpose of the hearing was not immediately clear.
The request came Friday afternoon in a letter from prosecutors who said they and defense attorneys sought a hearing but did not say why. The same letter also requested an extension of time for the defense to respond to pretrial motions.
The judge granted both requests and set the hearing for 3 p.m. at U.S. District Court in Central Islip.
Santos, who has pleaded not guilty to charges including lying to Congress and defrauding donors, is scheduled to go on trial next month.
Jury selection is set for September 9 with opening statements to follow on September 16.
* Get Eyewitness News Delivered
* Follow us on YouTube
* More local news
* Send us a news tip
* Download the abc7NY app for breaking news alerts