Former "Smallville" actress Allison Mack pleaded guilty Monday to racketeering charges in the case of the upstate New York self-help group that prosecutors say doubled as a secret sex cult.

Mack, 36, is facing up to 40 years in prison after she admitted to committing offenses that included extortion and forced labor in her role as a high-ranking member of NXIVM, according to the office of the U.S. Attorney in the Eastern District of New York.

A weeping Mack referenced the group's spiritual leader, Keith Raniere, as she apologized for her part in recruiting women into the organization.

"I believed Keith Raniere’s intentions were to help people, and I was wrong," Mack said in federal court in Brooklyn, according to the Associated Press.

"I can and will be a better person," she added.

Mack was among six people indicted last year for their roles in running the controversial group led by Raniere, who prosecutors say operated a master-slave ring within the organization with the help of the TV actress.

As part of the secret group inside NXIVM, known as DOS, women were pressured to have sex with Raniere and brand his initials into their flesh, court papers say.

Keith Raniere, second from right, leader of the secretive group NXIVM, attends a court hearing on April 13, 2018, in the Brooklyn borough of New York. Elizabeth Williams / via AP file

NXIVM supporters say it was a self-help group committed to changing the world. Prosecutors have described it as a criminal enterprise built around a pyramid scheme designed to enrich the top officials and supply Raniere with a stable of sex "slaves."

Two defendants, Nancy Salzman and her daughter Lauren, have already pleaded guilty in the case.

Raniere, who was known inside the organization as "Vanguard," was hit with child pornography charges last month. He had already pleaded not guilty to racketeering, trafficking and conspiracy charges.

Raniere is expected to go on trial later this month. Others indicted in the case include NXIVM accountant Kathy Russell and Seagram's liquor heiress Claire Bronfman. They have all denied the allegations.

Mack is set to be sentenced on Sept. 11.