The French telecoms regulator ARCEP said it had asked prosecutors to investigate Microsoft Corp’s Skype for failing to register as a telecom operator.

Skype has not complied with the regulator’s repeated requests to register as an “electronic communications operator”, ARCEP said in a statement on Tuesday.The regulator said that since Skype let users make voice calls to fixed and mobile numbers in France and around the world, it had an obligation to allow emergency calls and permit legal interception of calls when required.

Voice over Internet players like Skype offer calls for free or at a fraction of the cost charged by traditional telecom operators and have been growing rapidly in recent years.European telecoms companies have had to deal with shrinking mobile bills as consumers switched from voice calls to apps such as Skype, What’s App and Viber, which let them communicate for free using their mobile data plans.