Slim's America Movil wins telecom battle in top Mexico court

(Adds company statement)

By Noe Torres, Julia Love and Sheky Espejo

MEXICO CITY, Aug 16 (Reuters) - Mexico's Supreme Court on Wednesday ruled billionaire Carlos Slim's telecommunications company America Movil should not be barred by law from charging competitors certain fees, prompting fears of a rollback of a sweeping antitrust reform.

The 2014 telecom industry reform, one of Mexican President Enrique Pena Nieto's signature accomplishments, prohibited America Movil from charging other carriers for calls made to customers on its network, even though those firms are allowed to bill America Movil for using their networks.

The reform was aimed at breaking up Slim's market dominance, which rivals said made it challenging for them to break into the sector. It was one of several changes, along with an opening of the state-run energy industry, that have increased competition in Mexico's strategic industries.

The Supreme Court ruling said the so-called interconnection rates should be set by telecom regulator IFT, siding with America Movil - Latin America's largest telecom firm by number of subscribers and the crown jewel of Slim's empire. Tariffs set by the IFT will take effect from January 2018, the court said.

America Movil hailed the ruling in a brief statement late on Wednesday, calling on the IFT to set interconnection rates that are "oriented toward costs, transparent and reasonable."

In its ruling, the court also said, however, that the ruling would not have "retroactive effects," suggesting competitors such as AT&T Inc and Telefonica would not have to reimburse America Movil for the time they did not pay.

"The (IFT) will be responsible under its constitutional mandate for recognizing the asymmetry, establishing regulation regarding rates, the so-called 'zero-rate' or whatever else it defines, in line with the exercise of its constitutional faculties," Minister Javier Laynez Potisek said during the court's session.

The decision worried foreign companies, which have invested heavily in the market since the reform. Telefonica voiced grave concerns, saying the ruling had "serious consequences for the sustainability and makeup" of the sector.

In a possible sign of the pressure the regulator will come under as it ponders whether to allow America Movil to charge, the Spanish company said it and others had been severely hurt by the decision and called on Mexican authorities to find a balance.

The office of the president said it respected the court's decision and trusted that the regulator would use its powers to strengthen competition in a sector it described as key to the country.