Internet service providers should ask surfers' permission before using their traffic data for advertising purposes, according to the Center for Democracy & Technology (CDT).

The US pressure group said that consumers should be able to say no to having their web traffic analysed to target specific adverts.

The comments were made as the Network Advertising Initiative updates its self-regulatory code of conduct for online behavioural advertising, taking into account input from outside organisations.

"CDT suggests that ISPs engaged in such practices be required to provide unavoidable notice and obtain affirmative, express opt-in consent," an official CDT statement said.

The group also asked that ISPs display ongoing notice of these practices, and that when consumers revoke their consent their internet traffic data should no longer be collected.

CDT said it had welcomed the original NAI principles when they were issued in 2000 as an important first step, but saw room for improvement even in the initial version.

"We had hoped that the NAI would regularly update its principles and, in recent years, as technological evolution has accelerated and consolidation among online advertising companies has taken hold, we have urged the NAI to revisit its principles to resolve the issues present in the original version and to address emerging issues in the marketplace," the CDT statement said.

CDT also said it remained unclear how the NAI principles would interact with the US Federal Trade Commission's current work on guidelines for behavioral advertising self regulation.