The South Australian police force has accused controversial NSW magistrate Pat O'Shane of overstepping her authority by ordering the arrest of one of its officers.
Ms O'Shane on Tuesday issued a warrant for the arrest of policewoman Charmaine Peters, after SA authorities failed to comply with a subpoena in a child pornography case.
Senior Sergeant Peters wrote a letter on behalf of the police in response to a September 2 request for evidence by lawyers for Kenneth Asplund.
She detailed a response to the subpoena but did not provide the evidence requested.
Asplund, 63, of Bargo, is due to face a committal hearing in Sydney's Downing Centre Local Court for possessing child pornography and grooming a child younger than 16 for sex over the internet.
SA police made an emergency application to the NSW Supreme Court to have the arrest warrant for Snr Sgt Peters stayed overnight, after Ms O'Shane knocked back an application to temporarily freeze her order.
Robert McIlwaine, appearing for Sen Sgt Peters on behalf of the NSW Crown Solicitor's Office, told the court he would press for the order to be permanently quashed.
Asplund's lawyer, Christopher Blood, told Justice Peter Hall the evidence Asplund was seeking from the SA police was vital to preparing his defence.
Mr Blood defended Ms O'Shane's decision to issue an arrest warrant, saying it was in the interests of justice.
But Mr McIlwaine said the magistrate had exceeded her authority.
"The magistrate had absolutely no power to issue a warrant for a person not named in a subpoena," he said.
"(This is) an unlawful warrant which would expose those who arrest (Snr Sgt Peters) to significant liability."
Although the sergeant had responded to the subpoena, Mr McIlwaine said she was not formally the person, at law, to which it had been directed.
It was therefore an error of law, and denial of natural justice, to issue a warrant for her arrest in the matter, he said.
"Simply, the power to issue the warrant cannot be enlivened," he said.
Justice Hall agreed with Mr McIlwaine's submission that temporarily overruling the arrest order could not prejudice Asplund, and directed the warrant be stayed until further notice.
The judge ordered Mr McIlwaine to immediately serve all papers in his case upon Ms O'Shane, and he set down the application for the order to be quashed for hearing at noon on Thursday.
Ms O'Shane is known for her controversial rulings, including the dismissal of charges against a man accused of yelling "Youse are f***ed" at the police.
Former NSW Police Minister John Watkins once called her a "serial offender when it comes to people in uniform," with "ongoing... prejudice against the police of this state."