Image caption BNP Paribas is among the 11 banks fined

France's competition authority has fined 11 French banks 384.9m euros ($504m; £323m) for colluding to fix the price they charge for handling cheques.

They charged an unjustified fee of 4.3 cents on 80% of cheques exchanged in France from January 2002 to July 2007, the Autorite de la Concurrence said.

It added that the banks were still charging two additional fees for "related services" that were not proportionate to the costs incurred.

The banks include BNP Paribas and HSBC.

The others are Banque de France, BPCE, Banque Postale, Confederation Nationale du Credit Mutual, Credit Agricole, Credit du Nord, CIC, LCL and Societe Generale.

The competition authority said the banks put up their fees during the transition towards the new digital system for processing cheques.

The banks argued that they had to compensate for a loss of revenue, as they were losing out on interest payments because they had to release the funds for the cheques sooner than under the previous system.

But the authority said there was no evidence that the transition to the new system had resulted in net losses for the banks involved.

"When the new digital system for processing and clearing interbank cheques was set up, the main French banks met and colluded so as to define together the functioning details of the new system," it said.

It noted that the banks stopped charging the 4.3 cent commission - paid by the remitting bank to the drawee bank - in 2007 "under the pressure of the ongoing proceedings".