Last March, five women gathered in a home near here to enter a secret sisterhood they were told was created to empower women.

To gain admission, they were required to give their recruiter — or “master,” as she was called — naked photographs or other compromising material and were warned that such “collateral” might be publicly released if the group’s existence were disclosed.

The women, in their 30s and 40s, belonged to a self-help organization called Nxivm, which is based in Albany and has chapters across the country, Canada and Mexico.

Sarah Edmondson, one of the participants, said she had been told she would get a small tattoo as part of the initiation. But she was not prepared for what came next.

Each woman was told to undress and lie on a massage table, while three others restrained her legs and shoulders. According to one of them, their “master,” a top Nxivm official named Lauren Salzman, instructed them to say: “Master, please brand me, it would be an honor.”

A female doctor proceeded to use a cauterizing device to sear a two-inch-square symbol below each woman’s hip, a procedure that took 20 to 30 minutes. For hours, muffled screams and the smell of burning tissue filled the room.

“I wept the whole time,” Ms. Edmondson recalled. “I disassociated out of my body.”

Since the late 1990s, an estimated 16,000 people have enrolled in courses offered by Nxivm (pronounced Nex-e-um), which it says are designed to bring about greater self-fulfillment by eliminating psychological and emotional barriers. Most participants take some workshops, like the group’s “Executive Success Programs,” and resume their lives. But other people have become drawn more deeply into Nxivm, giving up careers, friends and families to become followers of its leader, Keith Raniere, who is known within the group as “Vanguard.”

Both Nxivm and Mr. Raniere, 57, have long attracted controversy.