The European Commission will propose legislation in coming weeks to bring EU mobile phone roaming charges further into line with national tariffs, EU sources told Reuters Thursday.

The move promises to further crimp the margins of major mobile telecoms providers in Europe, such as Britain's Vodafone , Spain's Telefonica, Germany's Deutsche Telekom and France Telecom.

But it also promises to raise the spirits of the more than 500 million mobile phone subscribers in Europe, many of whom have experienced bill shock after returning from trips abroad.

Sources in the mobile industry described the new proposals as significant, with one saying Kroes was not being mild with the industry. Telecoms providers have challenged EU roaming regulations in the European Court of Justice but lost.

According to a draft of the proposal, expected to be approved by June, price ceilings imposed on mobile telecoms operators in recent years will be further lowered for voice calls and text messages sent while roaming.

A cap will also be introduced on retail data roaming, meaning telecoms operators will be forced to set a limit on the cost of downloading data from a device while abroad, the sources said.

Travelers' data-roaming bills have been limited since last year to 50 euros ($71) per month to avoid excessive billing -- unless a customer requests a higher or lower limit.

The move was made after the high-profile case of a German traveler who downloaded a TV program while roaming in France and later received a bill exceeding 46,000 euros.

Under the new proposals, sources said the cap on the cost of roaming voice calls in the EU would be lowered to 24 cents per minute from July 2014, a reduction of nearly 40 percent from the current cap of 39 cents.

From July 2016, higher roaming costs would be effectively be abolished for voice calls, the sources said. Text messages will be capped at 10 cents per SMS until July 2016, compared with the current ceiling of 11 cents.

(Editing by David Holmes)

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