Three of France's leading mobile phone firms have been fined a total of 534m euros (£364m; $630m) after being deemed guilty of market collusion.
Consumers were damaged by the firms' actions, it is claimed
France's Competition Council concluded that Orange, SFR and Bouygues Telecom shared commercial information between themselves, distorting competition.
Orange France has been fined 256m euros while SFR and Bouygues have been handed 220m and 58m fines respectively.
The three firms have denied that they compared and fixed their prices.
The fine is the largest single penalty levied by the competition watchdog.
In 2000, it fined eight banks a total of 174m euros.
COMPETITION COUNCIL FINES
Orange France: 256m euros
SFR: 220m euros
Bouygues Telecom: 58m euros
The Council said the three firms had regularly exchanged commercial information about the mobile market between 1997 and 2003.
This enabled the firms to protect their position in the market, the Council said, to the detriment of consumers.
Their actions had caused "significant damage" to the economy, it added.
The three firms may appeal against the verdict, which followed a lengthy inquiry by the competition regulator.
Orange is owned by France Telecom while SFR is owned by Vivendi Universal.
France Telecom is already appealing against a 80m euro fine, imposed earlier this year, for barring access to the wholesale broadband market.