Intel's European headquarters in Swindon and Munich were raided last week by officials from the European Commission investigating anti-trust allegations against the chip company.
The chip maker's customers, including PC manufacturers and distributors, were also raided by commission officials.
The EC launched an inquiry earlier this year after an investigation by Japanese regulators found that Intel had acted in an anti-competitive way in the Japanese processor market.
Intel said, "EC officials conducted a search of Intel Swindon and Munich on 12 July, as part of an investigation. Intel's normal practice is to attempt to co-operate with authorities from regulatory agencies and we are doing so in this case. Intel believes its business practices are both fair and lawful. "
In addition to the EC investigation, rival chip-maker AMD is suing Intel, claiming it acted in an anti-competitive way by pressurising 38 system manufacturers to use its processors. Intel denies the charges.
Angelo Basu, barrister and senior associate in law firm Pinsent Masons' competition team, said, "This is potentially very serious for Intel." The EC would not conduct a dawn raid more than four years after it began its formal investigation, without good reason, he added.
"Microsoft was fined nearly E500m (£343m) by the EC for abusing a dominant position in the EU which demonstrates how seriously it views such activity."
Michael Azoff, senior research analyst at Butler Group, said, if it were proven that Intel acted anti-competitively, it would mean that AMD and other chip manufacturers could have grown, and increased their R&D spending: PC prices might have been lower if it were proved that the market had been distorted.