Journalists should not be exempt from metadata retention laws on the off chance there are pedophiles within media ranks, the head of parliament's intelligence committee says.

It's an argument dismissed as offensive by the union representing journalists.

Controversial data retention legislation is expected to pass parliament's lower house on Thursday after the government struck a deal with Labor to create a public interest advocate to assess warrants for the metadata of journalists.

The media union has dismissed the proposal as a furphy warning that investigative journalism and the health of democracy are at grave risk if the bill is made law.

Joint intelligence and security committee chairman Dan Tehan is unapologetic.

In his books community safety must be the government's top priority and he believes the right balance has been struck.

Mr Tehan said his committee had been wary of making specific groups such as journalists exempt from metadata retention.

"For instance what happens if a journalist is a pedophile?" Mr Tehan told AAP.

"Are you telling me that there has been no journalist in the history of journalism who has ever committed a serious crime."

Mr Tehan acknowledged all the journalists he knew were "very good, honest hard-working decent people".

"The sad fact of life is that with every profession, you can't 100 percent guarantee there's not elements (of criminality)," he said.

Media Entertainment and Arts Alliance chief Paul Murphy says that argument is offensive.

"No one is suggesting journalists should be above the law, if they've committed a criminal offence of course they should be investigated," he told AAP.

But the special role of journalism in democracy had to be respected.

Mr Murphy has zero confidence in the proposed public interest advocate because proceedings would be conducted in secret behind closed doors.

Media outlets would not be told about applications for data or when authorities had accessed reporters' data.

"If the warrant system is going to have any credibility at all it's got to be contestable in court," he said.