By Karlee Weinmann ( December 5, 2013, 4:18 PM EST) -- Mexico's telecom watchdog fingered America Movil SAB and Grupo Televisa SAB as dominant marketplace forces in a preliminary report, a finding that Bloomberg said Thursday could force the companies to shed assets. The judgment is the first in a series of steps the Federal Telecommunications Institute has undertaken in order to foster more competition. America Movil, controlled by billionaire Carlos Slim, serves about 70 percent of Mexico's cellphone users and roughly 80 percent of its landlines. For its part, Televisa caters to around 70 percent of the country's TV subscribers. Under a new law, America Movil and Televisa can challenge the report....