The 37-year-old actress was named as a defendant in the lawsuit, which accuses the previously billed self-help company of being a Ponzi scheme, as well as exploiting female members and illegally experimenting on humans.
Keith Raniere, who founded NXIVM, was included in the lawsuit, along with 11 other members.
According to legal papers, obtained by Entertainment Tonight, the defendants "exerted power over the plaintiffs; took their money; made it financially, physically and psychologically difficult, and in some cases impossible, to leave the coercive community; and systematically abused plaintiffs physically and emotionally."
Responding to the lawsuit, Raniere's lawyer said in a statement: "The recently filed civil suit shows that several of the plaintiffs who appeared as witnesses at the criminal trial were less than candid when they testified under oath they were not going to sue Raniere."
"Clearly, these people were motivated by money, a motivation the jury should have known. This will be one of several issues we will raise in court."
Raniere, Mack and several other defendants were due to be sentenced on charges of their involvement in the cult earlier this month (January 2020). However, Brooklyn Federal Judge Nicholas Garaufis cancelled the January 17 sentencing and postponed it to a later date, which has yet to be determined, claiming that the report recommending a sentence for Raniere still isn't ready.
Mack has pleaded guilty to charges of sex trafficking and racketeering in relation to her involvement in the NXIVM organisation.