Monti invited companies to make formal complaints after having received numerous informal comments from telecom operators, he said.
The European Commission, the executive body of the European Union, is already examining two suspected breaches of antitrust law by telecom operators. One case, opened last year, concerns French Internet service provider Wanadoo, a subsidiary of France Télécom. The other, opened in May, is against Deutsche Telekom.
Monti said the complaints already received go far beyond these two cases.
"We are ready, of course, to [deal with] the additional complaints that could be filed on local loop unbundling," Monti said.
He is particularly concerned about cases where incumbent telecom operators are, allegedly, discriminating against new entrants, he said.
Competition Commission spokeswoman Amelia Torres said the allegations made in informal complaints pointed to a "pattern of discrimination" by incumbents across the 15 member states of the European Union.
The discriminatory behaviour is not necessarily to do with pricing, but is more about the conditions facing new entrants, such as the ability to install their equipment in incumbents' local exchanges, she said.
Some incumbents are alleged to have been causing "unjustified delays" in installing equipment and to be providing inferior services to new entrants, she said.
Only 4% of the local loop in the EU has so far been unbundled, according to the European Telecommunications Network Operators' Association (ETNO).