Australian Communications and Media Authority (ACMA) said Sydney radio station 2Day FM has applied to the Federal Court for an order to stop ACMA from continuing its investigation into the station's decision to play the phone call when the nurse gave information about Kate Middleton's treatment for serious morning sickness.
Nurse Jacintha Saldanha, who transferred the call to the ward at London's King Edward VII's hospital where the Duchess of Cambridge was receiving treatment, committed suicide a few days after the prank received worldwide attention.
But the station was scrutinised earlier this month following its decision to award a 'top jock' national prize to Christian.
ACMAM is looking into if the prank breached the station's broadcasting licence and the commercial radio codes of practice by using a surveillance device to record the call, according to reports in Australian media.
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ACMA said that it intends to fight the application to have the investigation blocked.
The Sydney broadcaster has filed a New South Wales Federal Court application arguing that ACMA has no power to continue a key part of its ongoing probe.
The radio station has also argued that the ACMA has no power to decide whether use of the surveillance device constitutes an offence and said that police have not investigated the case.
"The ACMA has no power to investigate whether the recording of a telephone call breaches state or federal laws," 2Day FM's parent company Austereo said in a statement.
"The agencies which do have that power have not conducted an investigation or sought any information from Today FM," it said adding "Today FM also considers that the recording of the prank call did not breach any law.