The Wikimedia Foundation has asked Phorm to exclude all its domains and websites - including Wikipedia - from Phorm's BT trials, because it considers such scanning to be an infringement of its users' privacy.
Phorm's automated reply said it was likely the ban would go into effect within 48 hours.
Earlier this week Amazon took the same view and asked Phorm to refrain from scanning its pages.
The Open Rights Group welcomed the bookseller's decision. The ORG has written to Microsoft, Google, Facebook, AOL/Bebo, Yahoo! and eBay asking them to take similar action and protect their users.
Phorm runs a system to allow webmasters to get their sites excluded from its trials.
The company suffered another blow this week when the European Commission announced infringement action against the UK government for failing to take action over secret trials run by Phorm and BT.
There has also been criticism of the dual role of Kip Meek - Phorm director and adviser to the Department for Business, Enterprise and Regulatory Reform. ®