Two followers of the conservative Catholic group Opus Dei are going on trial in Paris accused of forcing a disciple to work for more than a decade with little or no pay.
Defence lawyers portray it as a case about labour law, and an Opus Dei spokeswoman says that the plaintiff chose of her own will to follow the group.
But the trial is expected to shine a spotlight on the secretive group's practices.
Dan Brown's best-seller The Da Vinci Code painted Opus Dei as a murderous, power-hungry sect, a portrayal that the group vigorously rejected.
Opus Dei's founder, Spanish priest Josemaria Escriva de Balaguer, was made a saint by Pope John Paul II.
Today's trial comes after legal complaints filed by Catherine Tissier, who was 14 when she joined the Donson hotel school in eastern France, where the religious sacraments were led by Opus Dei.
Under the guidance of what she calls a "spiritual director," she gradually chose to follow Opus Dei's spiritual path and began working as a "numerary assistant".
"I was working from seven o'clock in the morning to ten o'clock in the evening every day, seven days a week. The three weeks of holidays we had were spent with Opus Dei where they thought us theology and pursued in-depth studies on the spirit of the (Opus Dei) founder," Ms Tissier said.
She said she never saw the money owed to her.
She was diagnosed with depression. A doctor, whom she said was an Opus Dei follower, put her on medication.
"I wasn't able to eat by myself, I couldn't even wash by myself, my head was hard to keep straight. Regardless of that, I still had the same workload in the Donson school," she said.
At age 29, she weighed just 39 kilos (86 lbs). During a weekend visit to her parents' home, they took her to see their family doctor, who said she shouldn't go back.
She first filed a lawsuit in 2001 accusing Opus Dei of "mental manipulation". Those charged were later dismissed.
Two Opus Dei followers and the association that employed her are going on trial on charges of "clandestine work" and "remuneration contrary to dignity".
"This isn't a crusade against Opus Dei, that's not what's at stake," her lawyer Rodolphe Bosselut said. His client wants compensation.
Thierry Laugier, lawyer for ACUTE, the association that employed Tissier at the hotel, said the case revolves solely around an alleged breach of labour law.
Beatrice de la Coste, spokeswoman for Opus Dei in France, said: "Catherine Tessier was an employee at the hotel school, she was of course in contact with Opus Dei and she chose that spiritual path."
Opus Dei had as of 2005 some 4,000 numerary assistants, all women, whose full-time, paid jobs are to care for the Opus centres, doing laundry, cleaning and cooking for the numeraries and priests who live there.