United States authorities have accused Mack of recruiting women to join what purported to be a female mentorship group but was actually a secret society run by Raniere, the leader of a network of purported self-help groups based in Albany, New York, called Nxivm.
Mack, 35, pleaded not guilty at a brief hearing in federal court in Brooklyn before US Magistrate Judge Cheryl Pollak.
The Smallville actress, along with NXIVM cult leader Keith Raniere, also known as "Vanguard", was charged with sex trafficking, sex trafficking conspiracy and forced labor conspiracy, according to the U.S. Attorney's Office Eastern District of NY.
The women were pressured into providing "collateral" before they could join the elite secret society, providing naked pictures, sensitive information about themselves and loved ones, and even rights to their assets.
The women were taught that the society would empower and strengthen them, according to prosecutors. Raniere was arrested on March 25 at a villa near Puerto Vallarta, Mexico on charges of sex trafficking, sex trafficking conspiracy and forced labor conspiracy.More news: Saquon Barkley's agents don't want him to go to Cleveland
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The existence of the group's darker side came to widespread attention in October 2017, when the New York Times published a story including interviews with former members and their families. He is being held without bail. She was said to have "slaves" underneath her and was accused of directly or implicitly required two women "to engage in sexual activity with Raniere".
Mack is said to have been at the highest level of the pyramid just below Raniere, actively coercing women into lower levels of the scheme.
In late March, Ms Mack's Smallville co-star Kristin Kreuk - who played Lana Lang on the show - was forced to issue a denial of rumours she had acted as a recruiter for Mr Raniere.
The charges are in connection with their involvement in NXIVM ("Nexium"), a group started by Raniere that claims its mission is "to raise human awareness, foster an ethical humanitarian civilization, and celebrate what it means to be human".
NXVIM is "an acronym for a Latin phrase that loosely translates to 'Lord/Master of the Obedient Female Companions, '" the U.S. Attorney's Office said. Another actress, Sarah Edmondson, has previously spoken out about the abuses she suffered within DOS and corroborated Kreuk's statement. He has since been moved to federal custody in Brooklyn and remains in custody.