The Dutch competition authority Nederlandse Mededingingsautoriteit (NMa) imposed fines totalling €88m (£57m) on the operators, claiming they had colluded to establish the size of subsidies for mobile phones at a meeting in July.
"If the operators had individually decided to cut handset subsidies, we wouldn't have taken action, but because they agreed to do so as a group, this violated competition rules," said a NMa spokeswoman.
Mobile phone operators have used handset subsidies to attract new customers, but with more people now owning mobile phones, operators in many parts of Europe have been trying to slash the costly subsidies.
The collusion fines are among the highest yet in Europe.
The largest penalties went to the largest Dutch operators, KPN Mobile and Vodafone Libertel, which were fined €31.3m (£20m) and €24m (£16m) respectively.
Ben Nederland, a unit of Deutsche Télékom, was fined €15.2m (£9.9m), while Dutchtone, a unit of France Telecom, was fined €11.5m (£7.5m). O2 (Netherlands), a unit of MmO2 of the UK, was fined €6m (£3.9m).
NMa expected most of the operators to challenge the decision, forcing Dutch courts to take action, according to the competition authority's spokeswoman. "If the courts get involved, a decision could take between one and two years during which time the operators don't have to pay the fines," she said.
Collusion among mobile phone operators has become a serious concern for European regulators who, in addition to handset subsidies, have been looking into what they view as excessive fees for international roaming calls and connecting calls from fixed-line networks to wireless networks.