"The preliminary investigation has revealed evidence of illegal behaviour," by Switzerland's national news agency, the Comco commission said.
The investigation will seek to show whether SDA-ATS has abused its dominant position and if it has impeded competitors.
The investigation so far has revealed evidence that the price system of the SDA-ATS was "designed to weaken the competition to push them out of the market," Comco said.
It also found the news agency prevented market entry of other news agencies in Switzerland.
"The Competition Commission examined in particular the circumstances that led to the cessation of business rival AP SDA Switzerland in February 2010."
"The discount policy of SDA-ATS, including through exclusive, and combined offers, is at the forefront of the investigation," the commission said.
The editor of SDA-ATS Bernard Maissen told AFP: "SDA-ATS, as the national news agency, owned by Swiss media, attaches great importance to equal treatment of all media and a transparent tariff system."