Attorney-General George Brandis has written to the House of Representatives committee on social policy and legal affairs, saying it would be inappropriate for the judges to give testimony on a "contested policy area".
"For reasons going to the heart of the separation of powers, I am of the view that the appearance of the judges before parliamentary inquiries about contested policy areas is rarely, if ever, appropriate,"
Senator Brandis wrote.
"For one thing, the subjection of judges to questioning by parliamentarians gives the impression that the judiciary is somehow subordinate to the legislature (even if a judge appears voluntarily). More importantly, members' questioning inevitably runs the risk of drawing witnesses into matters of political controversy from which the judiciary should remain separate."
The committee is looking at how the family law system could better protect and support people affected by family violence.
Hetty Johnston, executive chair of child protection advocacy group Bravehearts, said if the chief justices could not give testimony then the parliamentary inquiry would be "a waste of time".
"It's shown itself to be totally ineffectual. It's clear to everyone. Our argument is the inquiry was a waste of time because it can't ask the hard questions and this has been proven to be the case. Why is the taxpayer paying for this?" Ms Johnston said.
Ms Johnston and other family violence campaigners, including Rosie Batty are calling for a royal commission into the family law system.
Child protection campaigner Hetty Johnston says there is no point holding the family violence inquiry if the chief justice cannot give testimony. Photo: Peter Rae"The family law system is archaic, backwards and horrendously dangerous. A royal commission is the only legal instrument that's capable of overcoming all the obstacles," Ms Johnston said.
The committee asked Senator Brandis for his advice after the scheduled appearances of the chief justice of the Family Court, Diana Bryant, and the chief justice of the Federal Circuit Court, John Pascoe, were cancelled at short notice.
At the time, government ministers Greg Hunt, Alan Tudge and Michael Sukkar were facing contempt of court allegations after making comments criticising the Victorian judiciary for what they described as weak sentences given to terrorists.
The chief justices have made written submissions to the inquiry but members of the committee will not be able to question them about their submissions.
The committee's chair and Liberal MP Sarah Henderson said it was "prudent and appropriate" to seek Senator Brandis's advice.
"The Attorney-General appears to have drawn a distinction between judges appearing before parliamentary inquiries in their personal capacity and heads of jurisdiction appearing in relation to the operations or decisions of courts over which they preside," Ms Henderson said.
But the committee's deputy chair, Labor MP Sharon Claydon, said the advice was a "drastic and detrimental departure from a time-honoured practice of the Parliament".
"It's been standard practice for parliamentary committees to take testimony from judges about important legal matters. This testimony has long been crucial in helping committees to come to informed decisions and make effective recommendations. How can committees make recommendations about important legal reforms without speaking to the heads of jurisdictions that see the human face and consequences of these laws every day?" Ms Claydon said.
A spokeswoman for chief justice Bryant and chief justice Pascoe declined to comment.
A spokesman for Senator Brandis declined to comment.
This article was written by Stephanie Peatling and was copied from here.