Optus has been ordered to hand over the details of a customer accused of defamation over a Google review.

The telco's Australian office has been ordered to produce documents which could unmask the writer of the negative review on a Melbourne dentist’s listing.

The details are allegedly needed for defamation proceedings.

It comes after dentist Matthew Kabbabe's legal team successfully convinced the Federal Court to order Google to give up initial details that identified the user, known only as CBsm 23, as an Optus customer.

Dr Kabbabe's lawyer, Mark Stanarevic from Matrix Legal, said it is a big move.

“We've opened up the veil, pierced it, in terms of people hiding behind Google reviews,” Mr Stanarevic said.

“It's been demonstrated that we can do that now.

“It seems litigation is the only mechanism [where] people can seek these remedies.”

Optus has until June 17 to respond to the subpoena, and is yet to make any comment.

Matrix Legal lawyers have also succeeded in ordering Google to hand over any identifying details of a negative reviewer accused of defaming Melbourne gangland lawyer Zarah Garde-Wilson.

Mr Stanarevic said Ms Garde-Wilson suspected her anonymous reviewer was a competitor, if so, they could be sued under Australian consumer law for misleading and deceptive conduct.