The European Commission warned on Monday that mobile phone operators must meet the July 30 deadline by offering new roaming tariff or face fines.

"All roaming customers in the European Union have to be given the opportunity by July 30 to opt deliberately for the new euro-tariff," said Martin Selmayr, spokesman for the European Union's Telecoms Commissioner Viviane Reding.

Under the EU new roaming fee regulation, which entered into force a month ago, mobile phone operators had until midnight Monday to offer the new so-called roaming rates and until end of August must bring them into effect whether customers request them or not.

Selmayr said if companies fail to offer the option, which is "in breach of the regulation," customers could lodge a complaint or suit with national authorities, who may impose fines for non-compliance.

The European Commission will also name those companies on its official website, Selmayr said, adding that he estimated the great majority of European operators were implementing the new rules.

The EU new roaming fee regulation slashed the costs for EU mobile phone users to make or receive calls when they are in another member state. Under the regulation, the cap for outgoing calls made abroad will be 49 euro cents (66.15 U.S. cents) per minute. The cap will decrease automatically by 3 cents (4.05 U.S. cents) per year in the following two years after the entry into force of the regulation.

The cap for receiving calls abroad will be 24 cents (32.4 U.S. cents). It will drop to 22 cents (29.7 U.S. cents) after the first year, and to 19 cents (25.65 U.S. cents) in the following year.

All the prices are VAT excluded.