Criticism is mounting of telecoms company KPN for using software known as Deep Packet Inspection to monitor what extra services mobile internet users are accessing.
KPN said on Thursday it used DPI to monitor use of the WhatsApp application for smart phones but denied it analyses actual messaging and content. Vodafone has also admitted using DPI to monitor mobile internet use.
T-Mobile has not admitted using DPI but does say it keeps an eye on what bandwidth mobile internet users are taking up, to make sure there is enough capacity, news agency ANP reports.
KPN is planning to introduce extra fees for some mobile internet services, such as internet-based phone calls and DPI allows it to analyse what services customers are using.
Digital rights group Bits of Freedom believes KPN is violating the law and is calling on KPN subscribers to lodge legal complaints, website Wireless Federation said.
The consumers association Consumentenbond has called on the privacy watchdog to look into the use of DPI.
Telecoms watchdog Opta has already said KPN should not use the technology to analyse what its customers are doing online because there is enough other technology to achieve the same result. Opta too called on the privacy watchdog CBP to intervene.
The CBP has not yet responded.
DPI can also be used to offer targeted advertising and copyright protection.