Lawyers for 2Day FM have told the Federal Court that the media watchdog has no power to decide whether the radio station breached surveillance laws in the infamous royal prank call.
The radio station is trying to stop the Australian Communications and Media Authority (ACMA) from carrying out any further investigations into the 2012 hoax.
DJs Mel Greig and Michael Christian rang the London hospital where the Duchess of Cambridge was being treated for morning sickness last December, pretending to be the Queen and Prince Charles.
Nurse Jacintha Saldhana passed the call through to the ward and, after enormous publicity about the hoax, .
The Federal Court heard ACMA has written a preliminary report, which found that 2Day FM had breached its licence by carrying out the prank.
Barrister for the radio station Bruce McClintock said the report went further, finding the call had broken surveillance laws.
Mr McClintock is arguing ACMA does not have the power to find criminal guilt, yet has acted as investigator, judge and jury by making these preliminary findings.
He says federal police have already interviewed some 2Day FM staff and there would be "nothing more prejudicial" than if the report was released.
ACMA has rejected the suggestion and says it is always fair in these matters.
The case continues.