Actress Allison Mack, best known for her decade on TV's "Smallville," and Keith Raniere, the leader of what authorities allege is a sex cult, were indicted on Friday in New York on federal charges of sex trafficking and conspiracy to commit forced labour, the Albany Times-Union reported.

Raniere and Mack are each charged with multiple counts, and could face a minimum of 15 years in prison. Mack was arrested in New York City on Friday and will be held pending a bail hearing Monday. Raniere has been in custody since he was arrested in Mexico in March.

Raniere is the founder of NXIVM, which bills itself as a self-help and empowerment organisation, but is described by authorities as a cultlike group whose members recruited women to be sex slaves, and branded their pubic regions with Raniere's initials.

Allison Mack

Photo: AP

The Rochester Democrat & Chronicle said Mack was indicted "for her role in DOS, a group . . . that purported to be a women's empowerment sorority. Prosecutors, however, say DOS was actually a sex-slave ring led by Raniere, with women known as 'slaves' who reported to 'masters' who ultimately reported to Raniere himself. Mack is an alleged co-conspirator, reporting directly to Raniere."

Mack, 35, is alleged by prosecutors to have recruited slaves for pay, forcing the women to have sex with Raniere, and using explicit photos and damaging information to ensure their compliance.