Mexican regulators said the country's main television network and Carlos Slim's telecom company were "preponderant" market players and ordered them to open up to competitors.
Slim-controlled America Movil said it was reviewing the decision, which included regulations to eliminate national phone roaming charges and improve information for consumers and quality of service.
Televisa, which calls itself the biggest media outlet in the Spanish-speaking world, said the Federal Telecommunications Institute's "significant" restrictions included a demand that the network make its broadcasting infrastructure available to competitors through a public bidding process.
By declaring the Televisa network and America Movil "preponderant", authorities can impose restrictions on the companies to allow others to enter the sector dominated by a handful of telecom providers.
Currently, Televisa's only broadcast TV competitors are several government educational channels and the smaller TV Azteca, a former government network privatised in the 1990s.
Paradoxically for a move aimed at ending market concentration, the decision could open the way for Slim to get into television. America Movil controls about a 70 per cent of the market in cellular telephones and 80 per cent of land lines.
Televisa said it would be barred from buying exclusive rights to broadcast "programmes with unique characteristics" such as Fifa World Cup finals and Olympic Games.
Agustin Ramirez, president of the non-profit Mexican Association for the Right to Information, called the new rules "an important step in regulating highly concentrated markets".
Agence France-Presse, Associated Press