One of the developers of a widely used Canberra-based online mental health program said the new policy would affect the site's ability to provide anonymity and freedom from stigma.

But the Attorney-General's Department said the government was limiting metadata access to agencies with a clear operational or investigative need.

The Abbott government has introduced a bill to make it mandatory for telecommunications companies to store customer information for two years.

While it will not track the content of calls or emails, or website addresses, it could be used to track the sender, time and location of electronic communications, such as those from an online mental health site.

"I can't see a way that feeling safe and having privacy on the internet is compatible with knowing data about you is being systematically logged," National Institute for Mental Health Research e-hub group IT manager Anthony Bennett said.

Hundreds of thousands of Australians have been turning to online mental health websites for quick, simple and anonymous psychological assistance.

Mr Bennett said the new policy would be a barrier to people easily and anonymously accessing mental health services online.

"It doesn't actually prevent people from accessing these resources but it becomes another barrier to doing that safely," he said.

"There's a lot of stigma around mental illnesses and being able to seek information and help without necessarily having to disclose what's going on is a great benefit to these programs.

"The metadata which will be collected under this legislation doesn't provide for collecting websites . . . but other communications such as emails would fall under this system."

A spokesman for the Attorney-General's Department said the Data Retention Bill did not alter the "existing strong privacy protections for Australians' communications".

"Agencies may only request data where it is reasonably necessary for a prescribed purpose, and they must also consider the privacy impact of accessing such data," he said.

Australian Privacy Foundation vice-chairman David Vaile said the implications of metadata retention for Australians' online privacy were "massive".

He said the government's legislation would have flow-on effects for the use of online mental health services.

"First, it disproves the assumption that metadata is somehow less intrusive or less revealing than so-called content [screening] and, second, it gives you an illustration of what's been called the chilling panopticon effect," Mr Vaile said.

"That means the mere consciousness that you're being spied on and monitored, and who you see and what you do and what you read are being compiled in a secret dossier somewhere [changes how you use the internet]."

Mr Vaile said the evidence for metadata retention assisting in law enforcement was scarce.

"One question that's being asked is 'do these people even understand what they're playing with'? Do they weigh up or know the harm they're potentially causing?" he said.