Mexican regulators have fined billionaire Carlos Slim's Telefonos de Mexico company $52 million (657 million pesos) for blocking a competitor.

Mexico's anti-monopoly commission said Thursday that Telmex refused to connect local and domestic land-line calls to Mexican competitor Axtel for 10 months in 2009 and 2011.

This is the third time the commission has fined Telmex for the same type of violation.

Telmex controls nearly 80 percent of Mexico's fixed phone lines, and the commission says the refusal to connect Axtel to that network was a monopolistic practice.

Telmex is the dominant player in the field in part because it was a former government monopoly privatized in the 1990s.