Catherine T., who has asked not to be identified by her family name, said she joined a hoteliers' school in northeastern France in 1985, aged 14, which she later discovered was run by associates of Opus Dei.
She said she was forced to take vows and made to work as a domestic servant for virtually no pay. Opus Dei has said it was "not involved in the charges being brought" and had "nothing to be guilty about."
The organisation, which is branded a dangerous sect by some critics, came to wide attention after featuring in the blockbuster novel and film "The Da Vinci Code". The case comes after a nine-year investigation.
She said the group compelled her to take vows of obedience, poverty and chastity and for the following 13 years gave her jobs with organisations that her lawyer Rodolphe Bosselut said were linked to Opus Dei.
She said she was made to work 14-hour days, seven days a week, cleaning and serving. Staff paid her a salary and then reclaimed money from her by making her sign blank cheques, supposedly to pay her room and board, she alleged.
She added that staff accompanied her wherever she went, including on visits to the doctor. On these occasions she was taken to see an Opus Dei doctor who prescribed tranquilisers that left her "senseless".
Catherine weighed only 39 kilogrammes (86 pounds) in 2001 when her parents rescued her from the group. Lawyers first took legal action that year alleging "mental manipulation" among other charges.
The charges agains the two Opus Dei members and the University and Technical Culture Association (ACUT) -- which ran the school -- are for "undignified punishment" and for not declaring her as an employee.
The ACUT has said it has nothing more than a "cultural link" with Opus Dei.
The colleges's lawyer, Thierry Laugier, has previously said that "There is nothing to this case," and insisted that Catherine T. "was paid according to the work she did."