Mexico's anti-trust commission confirmed on Wednesday its earlier finding that Telefonos de Mexico SAB enjoys dominance in the market for completion of fixed-line telephone calls, potentially making Telmex subject to special regulation.
The panel, known as the CFC, voted unanimously to reject Telmex's appeal of aTel 2009 ruling.
Telmex and its Telnor subsidiary have "substantial power" over the competitors who must pay them for access to Mexico's largest fixed-line network, the CFC concluded.
While the decision does not "imply sanctions" for the companies, it does enable Mexico's telecoms regulator - Cofetel - to scrutinize Telmex and Telnor in regard to the interconnection rates they charge and the quality of service provided, the CFC said.
Competitors have long complained that Telmex's interconnection charges are excessive and the Organization for Economic Cooperation and Development says Mexico's rates for both fixed-line and mobile phone service are among the highest in the world.
Telmex is a unit of America Movil SAB, the cornerstone of billionaire Carlos Slim's business empire.