• This story was published in 2018.

An actress from the television series “Smallville” was charged on Friday with sex trafficking for her involvement in an organization promoting itself as a self-help group for women that forced its members to have sex with its leader, federal prosecutors said.

The actress, Allison Mack, 35, helped gain recruits for what was purported to be a mentorship group but instead exploited its followers, who were branded with a symbol containing the initials of the organization’s leader, said Richard P. Donoghue, the United States attorney for the Eastern District of New York, in a statement.

Ms. Mack participated in a group known as Nxivm (pronounced Nex-e-um), the authorities said. The organization, near Albany, was led by Keith Raniere, 57, who was arrested in March by federal officials in Mexico on sex-trafficking charges. Its followers were forced to have sex with him because they feared that if they did not do so, compromising material that they had provided about themselves would be released publicly, according to a complaint.

[Inside a secretive group where women are branded: Read our article on Nxivm.]

The group has denied it was a cult, but former members have said that Mr. Raniere demanded obedience from his followers, who referred to him as “Vanguard.”