A man jailed for 136 rapes could have his sentence increased after his case was referred to the Attorney General.
Reynhard Sinaga, 36, was found guilty of luring 48 men to his Manchester flat, where he filmed himself sexually assaulting and raping them.
The student, described as Britain's "most prolific rapist", was ordered to serve a minimum of 30 years in prison.
His case has been referred under the unduly lenient sentence scheme, the Attorney General's office confirmed.
The Crown Prosecution Service (CPS) said it had written to the Attorney General regarding the case.
"The case of Reynhard Sinaga is unprecedented in CPS history and we took a range of factors into account when bringing each trial to court," a spokesperson said.
"A key consideration was the likely impact on sentence of bringing further prosecutions and we are confident we did everything we could to ensure the court had adequate sentencing powers to see justice done in this case."
Sinaga targeted at least 190 victims and was "the most prolific rapist in British legal history", the CPS said when he was sentenced on 6 January.
Attorney General Geoffrey Cox QC has until 3 February to decide whether to seek a longer sentence for the Indonesian national.
Sinaga, who was a post-graduate student living in Manchester, would wait for men leaving nightclubs and bars before leading them to his flat in Montana House, Princess Street.
He drugged his victims before assaulting them while they were unconscious.
Judge Suzanne Goddard QC said he was "an evil serial sexual predator" who had shown "not a jot of remorse" during his trials, which took place across 18 months at Manchester Crown Court.
Mr Cox is due to make a decision about whether to send the case to the Court of Appeal by 3 February.