Lawyers for former International Monetary Fund chief Dominique Strauss-Kahn said they will challenge allegations he was involved in France with a criminal international prostitution ring.
Strauss-Kahn was named in preliminary charges March 26 in the case.
French authorities are investigating whether Strauss-Kahn was aware he had sex with prostitutes in 2010 and 2011 when he participated in orgies at parties organized by businessmen he knew.
If found guilty, he could face up to 20 years in prison.
Strauss-Kahn has admitted taking part in the orgies. But his lawyers say he did not commit a crime because he didn't know he was having sex with prostitutes.
The probe comes ahead of a New York hearing on March 27 in a civil case brought by a hotel maid who has accused Strauss-Kahn of sexual assault.
With reporting by AP and Reuters