Nationwide Building Society has contacted Phorm and asked it not to scan its website to collect data, in a decision aimed at protecting its customers' privacy.
Phorm's controversial technology tracks customers on the internet, monitors their behaviour and targets adverts at them.
"Our intension is to opt out of allowing Phorm to collect data about users on our website in order to protect the privacy of our customers," said a Nationwide spokeswoman.
Nationwide follows other companies in opting out its websites from the Phorm Webwise advertising system.
BT dropped Phorm's technology earlier this month. BT said it wanted to devote its resources to other services, but it would be watching to see how the use of Phorm's technology develops with other internet service providers.
Phorm said it is focusing on overseas markets such as South Korea, but it will continue to develop the service into a form that UK ISPs find useful.