Lawyers defending Peter Bartlett and Ron Sayers against tax fraud charges want to get their hands on documents showing why the mining contractors were subjected to secret Australia Crime Commission examinations.
Lawyer Chris Boyce told the Supreme Court yesterday they wanted to find out whether the crime watchdog acted at the behest of the Commonwealth Director of Public Prosecutions office.
Mr Bartlett, Mr Sayers and their co-accused, accountant Deborah Grace, have asked the Supreme Court to throw out tax conspiracy charges.
They claim their right to a fair trial was prejudiced by DPP officers getting access to material from forced ACC examinations.
The interrogations were conducted around the middle of last decade as part of the ACC's Wickenby probe. The three alleged conspirators were charged late last year.
Prosecutors and the ACC have rejected these claims, arguing the ACC's governing Act intended that information gathered before someone was charged could be shared with prosecuting authorities.
Mr Boyce said material gained in mandatory examinations should not be handed to prosecuting authorities if a person might be charged.
He said the official overseeing the examination should have given a direction to protect a fair trial.
Prosecutor Paul Roberts said on Wednesday it was "simply nonsense" to suggest material should not go to a prosecuting authority. "It's what they're there for - to look at all the material and make up their mind," he said.
Justice Eric Heenan reserved his decision.
If the judge finds a problem with DPP officers being given material from ACC examinations, there could be further evidence heard before he rules on whether to stop the fraud conspiracy charges.
A trial is scheduled for February.