EU regulators warned that they may take action against mobile phone operators who overcharge users for calls made abroad, an Associated Press report said.
The report quoted EU spokesman Martin Selmayr saying some European phone operators are fixing roaming fees by the minute instead of by each second of a call.
On average, users pay 24% more for calls they make outside their home nation and 19% more for calls they receive, he said.
Selmayr said EU Telecoms Commissioner Viviane Reding 'may tackle this issue' in draft rules to be presented at the end of September.
The GSMA Association, which represents most major telecom operators, said it was strongly opposed to rules fixing how companies bill customers, saying it was government micro-management that would hurt customers' choice of tariffs.
The EU last year capped the costs of mobile phone calls made and received in other EU countries but criticized operators for not making deeper cuts to average retail prices, the Associated Press report further said.
From August 30, the cap will fall again from â‚¬0.49 (US$0.72) to â‚¬0.46 to (US$0.68) for calls made and from â‚¬0.24 (US$0.35) to â‚¬0.22 (US$0.32) for calls received.
These prices do not include value-added tax, which is levied at different rates in each of the EU's 27 nations.
Regulators claim the EU move has brought real savings for customers as average prices have crashed from â‚¬1.15 (US$1.70) per minute in 2006.
But telecoms companies dispute the EU's claims that they generate unjustified profits from roaming charges, saying some are making losses that will hurt investment.