Telecom NZ has agreed to block access to websites known to contain child sexual abuse material using filter software funded by the New Zealand Government.
The digital child exploitation filtering system would be applied to Telecom-provided internet connections "in the coming weeks", the company said in a statement.
The system, which cost the NZ Government $150,000 this year, was made available to ISPs in March after a two-year trial.
The National Business Review reported the system was based around a customised version of NetClean software.
The paper also reported other ISPs' stance on using the filter with Orcon reportedly "the only high profile filtering holdout."
Telecom NZ had approximately 500,000 retail broadband customers, it said.
Telecom's retail chief Alan Gourdie said the filter did not negate parental responsibility.
He urged "continued supervision and monitoring of Internet use to keep kids safe online.
"We encourage Kiwis to keep their internet security up to date - Telecom's McAfee Security Suite includes parental controls and is free for all our customers with compatible operating systems," Gourdie said.
The Acting deputy secretary for NZ's Department of Internal Affairs, Craig Armitage, welcomed Telecom's decision to sign on.
"The filter is an important tool to reduce the demand for child abuse material currently available on the internet," he said.
"Telecom and other ISPs signing up are to be commended for taking this step."