A legal adviser to Europe's highest court Thursday recommended the court uphold a Europe-wide law forcing mobile operators to cut the rates they charge for using a mobile phone abroad.

Four of Europe's largest mobile telecom operators - Vodafone Group Plc (VOD), Telefonica O2, T-Mobile and Orange - have challenged the legal basis of the European Union's roaming regulation, passed in 2007, which mandated a substantial reduction in charges.

The regulation initially set a EUR0.49 cap for making calls and EUR0.24 for receiving call when travelling abroad, with further reductions annually to reach EUR0.35 and EUR0.11 respectively in 2011. It applies to all 27 countries in the European Union as well as Norway, Iceland and Liechtenstein.

Legal opinions such as this one are routinely prepared in cases heard at the European Court of Justice. A legal adviser with the title of Advocate General prepares a proposed ruling giving the judges hearing the case a review of the evidence and a reasoned argument from a fellow court member to consider. The opinion is not always followed in the final judgment.

-By Mike Gordon, Dow Jones Newswires; +352 691 180 766; mgordon.dowjones@gmail.com;