The family of Perth man Charles Zentai says an eleventh hour decision by the Federal Government to seek a High Court ruling on their father's long-running extradition battle, is disappointing and frustrating.

The Home Affairs Minister Brendan O'Connor will apply to the High Court for special leave to seek its determination on what constitutes a war crime, before the case can continue.

Mr Zentai, who turns 90 next month, is wanted in Hungary over the murder of a Jewish teenager in 1944 and has fought his extradition since 2005.

The Federal Court had previously ruled that Mr Zentai could not be surrendered to Hungary, because war crimes were not a criminal offence under Hungarian law in 1944.

The Home Affairs Minister Brendan O'Connor says it raises a significant issue for Australia's extradition regime.

Mr Zentai's son Ernie Steiner says his father, an Australian citizen, should not be used to resolve the government's extradition policy.

"There are many people in Hungary who are questioning the tactics and the value in pursuing these types of case when the evidence is so flimsy," he said.

Mr Steiner says he is disappointed the government will not support his father with better representation

"We hope someone will come to my father's aid," he said.

"My father can't afford to spend out anything more on legal costs so it would have to be done within certain constraints; pro bono or for legal aid rates."

abc.net.au