Bouygues Telecom is alleging that rival Free Mobile is throttling the data speed of its  subscribers when they roam onto the network of market leader Orange, said Les Echos.

Free is reducing the bandwidth available to its subscribers even before they hit their 3GB monthly cap, claims Bouygues, which is pursuing the matter in court.

Such a tactic would offer Free a saving on the roaming charges it pays Orange, so meaning it could compete more aggressively against rivals, including Bouygues.

And those roaming charges are significant — thought to be in the region annually of €500 million to €700 million.

The case is set to be heard by the Commercial Court of Paris on 18 December.

Bouygues says it has several studies to back up its case. One study shows how downloading video for Free subscribers is much slower on the Orange network than using its own infrastructure. On the former the time taken is more than 12 hours, while only seven seconds on its own network.

The two operators are tussling in a highly competitive market where Free has made ground through aggressive pricing tactics. Efforts to stabilise pricing through market consolidation have failed to deliver, so far at least.

Free has a roaming agreement in place with Orange that is designed to assist the newcomer’s entry to the market while it builds its own network. Bouygues alleges the country’s smallest operator is abusing that agreement.