Dutch broadband provider UPC is to introduce a new system in which its customers will pay more to access certain services and providers.
Critics have argued that the move could signal the end of net neutrality, unless it is contested by consumer groups or banned under the European Telecoms Reform package that entered the European Union conciliation procedure in May and will have its third reading this autumn.
UPC claims that the system, which will run from noon to midnight and will cut users' bandwidth by two thirds when accessing bandwidth-intensive services, will enable it to solve network problems and provide customers with faster access.
Under the proposals all protocols but HTTP will be capped to a third in peak times, and even some web sites that do use HTTP will be restricted if they take up too much bandwidth.
"Some recent changes in our network management settings have led to customer questions," said a UPC spokeswoman.
"[It is] important to know here that the changes are part of our continuous improvement of the network settings, and are not finalised as was assumed [in some press reports]."
She added that the changes would be finalised in the "coming weeks".
"We want to prevent the excessive internet usage by a very low number of customers - approximately one per cent - causing congestion for the other 99 per cent," the spokeswoman said.
Citizens rights groups such as La Quadrature du Net, meanwhile, have registered their concerns over the UPC plans.
"This is clearly harmful to the neutrality of the network. It shows bad network management. Legitimate networks divide all bandwidth among all users and, if the network is too small, they should invest in more bandwidth," said Jérémie Zimmermann, co-founder of La Quadrature du Net.
"This case determines the future of users' access to the internet. I expect there to be resistance from users and for some to leave the ISP."
However, Zimmermann said that the real danger is if other Dutch ISPs follow UPC's example. Consumers in the country would not be given a choice, and would have access only to a "sub internet" in which ISPs could favour partner web sites over competitors'.
The question of whether broadband operators should be allowed to restrict access to services and applications at their discretion has been a subject of hot debate between the European Parliament and Council this year.
During a vote in May on new European telecoms legislation, the Parliament refused for the second time to sanction any restrictions on net neutrality.
The Council and Parliament are currently trying to reach a compromise, and have scheduled a meeting to discuss the issue on 29 September.