MEXICO CITY (Reuters) - The Mexican government's consumer protection agency said on Sunday it had opened a class action lawsuit against Carlos Slim's fixed line phone company Telmex for making illegal charges.
Rafael Ochoa, a legal expert at the federal prosecutor's office for the consumer (Profeco), said Telmex had made unwarranted charges for a privacy service and that Profeco had filed the suit with a federal civil court in Mexico City.
Profeco took the step after noticing that Telmex was charging users some 10.40 pesos (55 pence) a month for a data protection service that was a constitutional right, said Ochoa.
It was unclear how many customers could join the suit and how much Telmex might be liable for, he noted.
"There's still not a precise estimate," Ochoa said, noting the period under scrutiny began in March 2012. He added that he expected a judge to rule on the case in around six months.
Telmex did not immediately respond to requests for comment.
Slim, the world's richest man, controls roughly 80 percent of Mexico's fixed line phone market and 70 percent of the country's mobile business through his giant phone company America Movil <AMX.XL>, of which Telmex is a part.
In February, Mexico's competition watchdog Cofeco said it would fine Telmex $52 million (34 million pounds) for monopolistic practices.
Slim's companies have successfully fought off a number of lawsuits in the past, but the billionaire is facing tougher regulation from President Enrique Pena Nieto's government.
On March 11, Pena Nieto unveiled the biggest planned shake-up of the Mexican telecommunications market in decades, a sweeping reform that aims to boost competition and give regulators the power to make dominant players sell assets.
(Reporting by Adriana Barrera and Dave Graham; Editing by Bernard Orr)