The actress, who was arrested by the Federal Bureau of Investigation in April of a year ago, was brought in on charges of sex trafficking, conspiracy of sex trafficking, and forced labor conspiracy in relation to the organization that she had reportedly been a part of since 2010.
Mack said that at the cult leader's instruction, she obtained compromising information and images of two unidentified women that she threatened to make public if they did not have sex with Raniere.
John Marzulli, Public Information Officer for the U.S. Attorney's Office for the Eastern District of NY confirmed Mack's plea, which was entered Monday.
On the surface, Nxivm offered self-help classes, but prosecutors allege that there was a secret sub-group within the organization known as DOS, an acronym that stands for a Latin phrase that loosely translates to "Lord/Master of the Obedient Female Companions". Mack pleaded guilty to racketeering charges on Monday in a case involving a cult-like group based in upstate NY.
There was no mention at the plea hearing of any agreement by Mack to cooperate with prosecutors against Raniere, who is expected to go on trial later this month.
Mack allegedly recruited girls for a secret society within NXIVM and founded by Keith Raniere, called DOS, or "The Vow", around 2015.
She is now scheduled to be sentenced in September and will face a maximum sentence of 20 years in prison for each of the two charges.
In a statement posted to her website in December 2017, Bronfman said, "There have been many defamatory accusations made and I have taken them seriously". Authorities said the women were branded by a surgical tool with a symbol that resembled Raniere's initials.
Prosecutors last month hit Raniere with additional charges for allegedly having sexual relationships with children and producing kiddie porn.
Raniere, who has been in custody since 2018, has pleaded not guilty to the charges against him. She pleaded not guilty at the time.
Clare Bronfman leaves Brooklyn federal court in NY on July 25, 2018.
Others facing charges include NXIVM bookkeeper Kathy Russell and wealthy Seagram's liquor heiress Clare Bronfman.