Strauss-Kahn was called in by investigating magistrates Monday, two days earlier than expected, and charged, Radio France Internationale reported.
Richard Malka, Strauss-Kahn's lawyer, has argued his client didn't know the women hired by hosts of parties in Washington and Paris were prostitutes and that Strauss-Kahn did not pay them, The New York Times reported
Strauss-Kahn has been barred from contacting defendants, plaintiffs, witnesses or the media, RFI said.
Eight people have been charged in the case, including a lawyer, a Lille police official and three executives of the Hotel Carlton in Lille.
Using prostitutes is not illegal in France, but prosecutors are trying to prove Strauss-Kahn knew the parties were set up by an organized prostitution ring and paid for by guests misusing company funds, RFI said.
Strauss-Kahn, once considered the leading Socialist Party contender to oppose President Nicolas Sarkozy in elections that begin in April, resigned as IMF leader after he was arrested in May in New York on attempted rape and other sexual assault-related charges stemming from accusations from a hotel maid.
The criminal case was dismissed after prosecutors questioned the maid's reliability.
At a hearing Wednesday in a civil suit filed by the woman, Strauss-Kahn's attorneys are expected to argue he is protected from the suit because he had blanket diplomatic immunity at the time of the incident, the Times said. The maid's attorneys said his diplomatic immunity doesn't extend to sexual assault.