Allison Mack, an actor best known for her role in the US TV show Smallville, has been charged with sex trafficking and conspiracy.
She has been accused of recruiting women as sex slaves as part of a secret society which portrayed itself as a self-help group.
She was also accused of having a high up role in the Nxvim group, which was run by Keith Raniere, 57, who also faces charges after being arrested last month and charged with sex trafficking.
Ms Mack was arrested on Friday and has since pleaded not guilty to all charges.
Prosecutors said she helped to recruit “vulnerable” women to the group.
They alleged that upon joining, the women were forced to have sex with Mr Raniere, branded with his initials and made to eat low-calorie diets to satisfy the leader’s alleged preference for thin women.
They claimed that the women were also made to give nude photographs, other personal information or rights to assets as collateral that could be used to threaten them with at a later date.
They alleged that Ms Mack received a variety of benefits, including financial ones, for recruiting others to the group, which has been described as a cult.
“Under the guise of female empowerment, she starved women until they fit her co-defendant’s sexual ideal, and she targeted vulnerable women,” Assistant U.S. Attorney Moira Kim Penza said at Friday’s hearing.
Ms Mack, who appeared at a brief hearing in federal court in Brooklyn before U.S. Magistrate Judge Cheryl Pollak, was denied bail but may be granted it later if she could offer “significant property”.
She is scheduled for a second hearing on Monday.
“The allegations contained in the indictment are only that, allegations,” Sean Buckley, a lawyer for Ms Mack, said at Friday’s hearing.
Marc Agnifilo, a lawyer for Mr Raniere, said earlier this month that he was “confident these allegations will be soundly disproven.”
Nxvim released a statement on its website which said: “In response to the allegations against our founder, Keith Raniere, we are currently working with the authorities to demonstrate his innocence and true character. We strongly believe the justice system will prevail in bringing the truth to light.
It said it was “saddened” by reports and added: “It is during the times of greatest adversity that integrity, humanity and compassion are hardest, and needed most.”
The group, which claims to be “working to build a better world” claims it is “a community guided by humanitarian principles that seek to empower people and answer important questions about what it means to be human”.
Fellow Smallville actress Kristin Kreuk also recently denied any involvement in the “inner circle” of the organisation. She said she took part in an Executive Success Program with NXIVM but left years earlier and said she was “deeply disturbed” to hear of the allegations.
Additional reporting by Reuters