The commission has reason to believe that the companies concerned may have violated EU rules on restrictive business practices it said, adding that its officials were accompanied by their counterparts from the relevant national competition authorities.
Surprise inspections are a preliminary step in EU investigations into suspected cartels.
The commission said the fact that it carries out such inspections does not mean that the companies are guilty of anti-competitive behaviour, nor does it prejudge the outcome of the investigation itself.
It noted there is no strict deadline to complete cartel inquiries and that their duration depends on a number of factors, including the complexity of each case, the extent to which the undertakings concerned co-operate and the exercise of the rights of defence.
Contacted by Thomson Financial News, Air France-KLM declined to comment on whether it is involved in the EU probe.
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