A last-minute request by the FBI to call witnesses to next week's court hearing in the San Bernardino iPhone case indicates the agency might feel some weakness in its legal arguments, Apple said.

On Wednesday evening, the FBI asked for an evidentiary hearing, which means the court will hear live testimony from expert witnesses from both sides. Apple agreed to the FBI's request on Thursday.

Speaking on Friday with reporters, lawyers for Apple said the FBI's request was a surprise, and they don't understand why the government wants to present witnesses to the court.

If lawyers believe they have a strong legal case, they typically want to argue it without bothering with witnesses in these types of hearings, so the request may indicate that the FBI isn't as comfortable as it was in relying solely on legal arguments, an Apple lawyer said.

Apple will present two witnesses: Erik Neuenschwander, its leading cryptography expert, and Lisa Olle, the Apple attorney who dealt with the FBI as it requested details from the phone.

The company plans to argue what it's been saying all along: that the All Writs Act, the late 1700s law the government has based its arguments on, doesn't allow investigators to push Apple to develop custom software that would give the FBI unlimited chances to break the passcode on the iPhone.

Some of the details surrounding Apple's dealings with the Justice Department in the case have been deemed confidential, but Apple lawyers said they hoped those restrictions would be lifted because of the request for testimony.

The hearing is scheduled to begin at 1 p.m. PDT on Tuesday in District Court for the Central District of California, and it is expected to run until around 5 p.m.