NEW YORK (CBSNewYork/AP) – “Smallville” star Allison Mack was arrested Friday morning.

Mack, 35, and Keith Raniere – also known as “Vanguard” – face sex trafficking and forced labor conspiracy charges.

Raniere, 57, was the leader of a secretive group accused of coercing female followers into having sex and getting branded with his initials.

Raniere ran a group called NXIVM – pronounced “Nexium” – and was previously arrested in Mexico and brought back to the U.S. to face charges.

Raniere sold himself as a self-improvement guru to the stars.

WEB EXTRA: Read The Indictment (.pdf)

“As alleged in the indictment, Allison Mack recruited women to join what was purported to be a female mentorship group that was, in fact, created and led by Keith Raniere,” said United States Attorney Richard Donoghue. “The victims were then exploited, both sexually and for their labor, to the defendants’ benefit.”

“Today we announce an additional arrest, and an indictment, in a case that brought to light an inconceivable crime,” said FBI Assistant Director-in-Charge William Sweeney.

A core group of disciples was drawn to Raniere, including actresses, wealthy heiresses and a son of a former president of Mexico. His followers were known as “Nxians,” and were “encouraged to pay for additional [NXIVM] classes and to recruit others to take classes in order to rise within the ranks of NXIVM,” prosecutors said.

Proscutors said NXIVM “maintains features of a pyramid scheme.” They allege Raniere created a secret society within NXIVM called “DOS,” in which “masters” held “slaves.” All members of the DOS group except for Raniere, who was at the top of the Master/Slave group, prosectors said.

“Many DOS slaves were branded on their pelvic areas using a cauterizing pen with a symbol which, unbeknownst to them, incorporated Raniere’s initials,” prosecutors said. “During the branding ceremonies, slaves were required to be fully naked, and a master would order one slave to film the branded while the others restrained the slave being branded.”

Mack allegedly “required her slaves… to engage in sexual activity with Raniere.”

Raniere and Mack each face a minimum of 15 years in prison and could get life if convicted.

In March, federal authorities raided an upstate New York residence near Albany where NXIVM was headquartered. The organization also ran programs in Mexico.

Raniere’s followers included Clare and Sara Bronfman, heiresses to the Seagram liquor fortune, and Emiliano Salinas Occelli, son of former Mexican president Carlos Salinas de Gortari, who with a business partner controlled the Raniere-linked Executive Success Programs in Mexico.

Catherine Oxenberg, who once starred on “Dynasty,” became connected to the group when she attended a meeting with her daughter several years ago. She has said she was turned off by it but her daughter remained a devotee.

“This is a very personal fight for me. He is where he deserves to be – behind bars for the rest of his life,” Oxenberg said last week.

“It’s very upsetting and nauseating to me,” said Stanley Zareff, a friend of Oxenberg. “I want to see her put away. She’s dangerous, she’s sick, she’s evil, she’s dark and she’s done harm to many people.”

Founded in 1998, NXIVM promoted Raniere’s teachings as a kind of mystical, executive coaching designed to help people get the most out of life. Enrollees in its Executive Success Programs paid handsomely for his advice, but the organization also drew criticism from people who likened it to a cult.

Last year, the accusations took a new twist, with women who were part of the DOS subgroup coming forward to say that they had been physically branded near their pelvises with a surgical tool against their will.

“This is just the beginning of what needs to happen to stop the reign of terror that Keith Raniere and NXIVM has,” said Raniere’s ex-girlfriend Toni Natalie.

Raniere’s lawyer, Marc Agnifilo, previously said his client is innocent.

“The facts will show that Raniere didn’t compel or pressure anyone to do anything and that everyone was acting in accordance with his or her free will at every instant,” he said.

Mack pleaded not guilty Friday but was sent to jail with no bail.

(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)