The Commerce Commission is fighting a High Court decision to decline their application for an interim injunction against controversial ticket reseller Viagogo.
The regulator was seeking an interim injunction to stop the Switzerland-based website from committing what it said were further breaches of the Fair Trading Act.
In February, Justice Courtney declined to issue the interim injunction because Viagogo had not yet been formally served.
An attempt to serve a formal injunction notice was made to the European company, but it insisted it had to be served in its jurisdiction - not in New Zealand.
The High Court has granted the commission leave to appeal the injunction decision to the Court of Appeal.
Commission Chair Dr Mark Berry said they appealed the decision because of the ongoing harm caused by Viagogo's marketing.
Since 2014, the regulator has received nearly 950 complaints and enquiries about Viagogo.
In 2018, 557 complaints were made, making it the most complained about trader in a single year for the commission.