LOS ANGELES - The Sheriff's Department opened an investigation Thursday into allegations that Paris Hilton received special treatment during her 23 days in jail for violating probation in an alcohol-related reckless driving case, authorities said.

The internal probe will examine whether the hotel heiress was given free access to a cordless phone instead of being forced to wait in line to use a pay phone at certain hours, sheriff's spokesman Steve Whitmore said.

Also under scrutiny are claims Hilton received a new jail uniform instead of the recycled ones given to many inmates and that her mail was delivered by a captain instead of inmate trusties, Whitmore said.

The allegations were brought to the attention of the department's union, the Association for Los Angeles Deputy Sheriffs, by its members, the Los Angeles Times reported Thursday on its Web site.

Whitmore said the claims differ from the department's own information about Hilton's incarceration.

"We're going to investigate it and get to the bottom of it and find out exactly what happened," he said.

A message left with a Hilton spokesman late Thursday was not immediately returned.

The department was also accused of granting Hilton special treatment when Sheriff Lee Baca released the 26-year-old from jail after only three days for medical reasons. She was sent back to jail after one night.