The Dutch competition authority NMa has raided the headquarters of phone companies KPN, and T-Mobile in The Hague as part of an investigation into illegal price-fixing.
A spokesperson for KPN said five staff were questioned during the raid.
According to Nos television, the raids were prompted by two whistleblowers: one is said to be a former director, another is currently on the board at one of the firms.
The investigation focuses on the prices for mobile and Internet telephony, Nos said.
One of the whistleblowers is alleged to have told current affairs show Nieuwsuur that he had made agreements. "There are few people who know the details of the price-fixing... I have worked with many of them.' The man is also said to outline how the agreements are made.
The second whistleblower told the broadcaster during meetings 'the directors discussed the optimum price for mobile internet for prepaid' users. 'Several months later, those prices were introduced."
In August T-Mobile followed KPN and Vodafone by introducing more expensive subscriptions for smart phone users. All three made the move to compensate for loss of income due to the rise in internet-based telephony and instant messaging.
Just before the summer break, parliament passed net neutrality legislation, which stopped telecoms firms charging extra fees for services like Skype.
The three companies were fined 10 years ago for exchanging information about agents' fees.
DutchNews.nl / Westonline