Former public services minister Georges Tron, who resigned when the scandal broke in 2011, faces accusations that "massage" sessions were a pretext for sexual assault by two former council employees in Draveil, south of Paris, where he is still mayor.
One of his deputies, Brigitte Gruel, is accused of being his accomplice.
Both deny the charges and Tron claims he is the victim of a far-right conspiracy.
The official reason judge Régis de Jorna gave for the surprise postponement was that the time allowed for the trial was not sufficient.
Media coverage questioned
But the defence had strenuously demanded putting off the trial earlier in the day, citing two events that allegedly undermined the court's authority.
The first was a TV documentary broadcast on Thursday evening in which one of Tron's accusers, Virginie Faux, was interviewed along with a witness who had not yet appeared in court.
Tron's lawyer Eric Dupond-Moretti sent a letter to France's broadcasting authority, claiming the programme was a "particularly serious infraction of the presumption of innocence", which was likely to affect the trial.
The second was a meeting called by de Jorna with the lawyers, during which the documentary was discussed and the judge expressed concern about the trial in remarks he believed to be off the record.
He complained about media coverage of his questioning of Faux the day before and hinted that it would have been better to have a woman hearing the case.
Although such meetings are usually confidential, Dupond-Moretti later quoted the judge in court, accusing him of discrimination and incapacity.
Shadow of Weinstein scandal
The trial was taking place in the shadow of the deluge of sexual assault accusations that have followed allegations against Hollywood moghul Harvey Weinstein.
Furthermore, the prosecution in this week's hearings seemed more energetic than in previous hearings.
In 2013 a court dismissed the case and, although an appeal court overturned that ruling the next year, it was against the advice of the then-prosecutor who called for dismissal.
This week prosecutor Frédéric Bernardo was described by Le Monde newspaper as "pugnacious and aggressive", an change in attitude that appears to have increased the defence's motivation.