European Union anti-trust officials this week launched surprise investigations of several telecoms firms suspected of abusing their positions in Internet services, including Orange, Deutsche Telekom and Telefonica.
The European Commission said in a statement that its anti-trust officials had made the "unannounced inspections" on Tuesday on suspicions the companies had abused a dominant market position.
The companies, which wholesale Internet access to smaller rivals, are suspected of abusing this position to thwart the emergence of competitors.
It gave no names but a spokesman for France's Orange said it was "currently the target of a probe by European Commission services" whose staff had visited several Orange sites. The investigation "could last several days", he said.
Spain's Telefonica did not specifically confirm the probe but said that "in relation to the inspections announced today by the European Commission, Telefonica is closely cooperating with the Commission as it is common practice in the company."
German Deutsche Telekom said it was "very surprised by these new probes into Internet communications."
The Commission said it "has concerns" the companies "may have violated EU anti-trust rules that prohibit the abuse of a dominant market position".
But it stressed that the unannounced inspections are only a preliminary look into suspicions of anticompetitive practices and do not imply that companies are guilty of such behaviour.
Deutsche Telekom said previous allegations of abuse of market position "proved to be without foundation" after enquiries carried out by national anti-trust bodies.
It also said that the market was dominated by US suppliers.
Orange also said it had been cleared of any such suspicion by a national probe.