By Darren Waters
Technology editor, BBC News website
The ad-serving system profiles the sites people visit online
Amazon has said it will not allow online advertising system Phorm to scan its web pages to produce targeted ads.
Phorm builds a profile of users by scanning for keywords on websites visited and then assigns relevant ads.
It has proved controversial because it scans almost all sites a user visits and there is an ongoing political debate about how a user gives consent.
Last month the Open Rights Group wrote to the world's leading websites asking them to opt out of Phorm.
Phorm has conducted trials with BT of its technology, which is marketed as Webwise. BT plans to roll out the service to users after analysing the results of the trials.
In a statement, Amazon UK said: "We have contacted Webwise requesting that we opt out for all of our domains."
The company declined to comment further on the reasons behind its decision.
In a statement, Phorm said: "There is a process in place to allow publishers to contact Phorm and opt out of the system, but we do not comment on individual cases."
Last month the Open Rights Group wrote to the chief privacy officers at Microsoft, Google/Youtube, Facebook, AOL/Bebo, Yahoo, Amazon and Ebay urging them to opt-out of Phorm.
Amazon is the first company to give any sort of response at all.
Jim Killock, executive director of the Open Rights Group, said: We expect more sites to block Webwise in the near future and also ISPs to drop plans to snoop on web users."
He said other sites - LiveJournal, mySociety and Netmums - had contacted the Open Rights Group to say they too would be blocking Phorm's technology.
Earlier this week the European Commission said it was starting legal action against the UK over its data protection laws in relation to Phorm's technology.
The European Commission has described the technology as an "interception" of user data and wants UK law to reflect more explicitly the need for consent from users in order for the service to be implemented.
At present, UK law only covers "intentional" interceptions and requires there only to be a "reasonable grounds for believing" that consent to interception has been given.