The bill signed by Pena Nieto yesterday imposes fee limits and infrastructure-sharing requirements on any company that controls more than half the market in sectors like telephones, Internet or television.
Companies judged to have "preponderant" market positions face limits on how much and who they can charge, what fields they can enter and what kind of exclusivity arrangements they can make.
Pena Nieto says the change will increase competition in radio and television and create more effective phone and internet services.