Telstra will appeal a ruling by the privacy commissioner forcing it to hand over the metadata​ of a Fairfax Media journalist, a decision the peak telecommunications industry group says will pave the way for law-enforcement agencies to gain yet more access to customer data.

The verdict from commissioner Timothy Pilgrim, published on Monday, ruled that Telstra had breached the Privacy Act by failing to provide Fairfax's technology editor Ben Grubb with access to his personal information.

The decision followed a 22-month stand-off between Mr Grubb and Telstra, which had refused to disclose the metadata​ it collected on him as a Telstra customer, despite routinely handing such information over to government agencies when complying with data requests.

But the Communications Alliance, which represents Telstra and other Australian telecommunications retailers, slammed the decision, saying the classification of Mr Grubb's metadata as "personal" information was "regulatory overreach" that would drive up costs for telcos in complying with the Privacy Act.

"In making this decision the privacy commissioner has stepped into the realm of setting policy, without any consultation with industry and seemingly without a mandate from government to extend the reach of regulatory obligations deep into the operations of communications service providers," the alliance said.

Further, it argued the decision would likely backfire by increasing the amount of personal data available to law-enforcement agencies, because some of the data Mr Grubb requested was not currently provided to them on the basis they were "very difficult to extract".

"If telcos have to provide this much broader suite of data to customers, it is likely only a matter of time before agencies will start asking for it as well," the alliance warned.

The federal government failed to clearly define the term "metadata​" in its recently passed mandatory data retention legislation, which requires telcos to retain customers' metadata​ for up to two years for the purpose of aiding intelligence operations.

Telstra chief risk officer Kate Hughes said the decision in Mr Grubb's case could extend the definition of personal data to "every single piece of data in our networks, regardless of whether the data reveals the identity or anything else about someone".

"We respect the role the privacy commissioner plays and we share his commitment to transparency, but we will be seeking a review of the determination," Ms Hughes said.

In August 2014, Telstra confirmed it had provided URLs to agencies without a warrant "in rare cases".

It did not name the agencies or how many times it provided information. "The last time we did so was in relation to a life-threatening situation involving a child more than 12 months ago," a Telstra spokeswoman said.

In a Senate inquiry discussing comprehensive revisions of the Telecommunications Interception and Access Act last year, outgoing ASIO chief David Irvine said to gain access to web browsing histories agencies such as ASIO needed a warrant.

Clarification: The paragraphs concerning Telstra divulging URLs have been amended for clarity.