Former prime ministers Julia Gillard and Kevin Rudd have been ordered to hand over to a royal commission documents relating to Labor's bungled home insulation scheme.
But the commission has yet to direct any individuals to front a hearing.
Commissioner Ian Hanger QC on Tuesday said 95 summonses to produce documents had been issued since December, when he was given the job of probing the economic stimulus scheme which led to the deaths of four workers.
However, while he confirmed the commission had had some preliminary discussions with possible witnesses, it was still working through documentary evidence.
A second public hearing is expected to be held in March, followed the first hearing on December 23.
Mr Hanger said a number of people had approached the commission with information about their involvement in the program.
The commission has the power to require people to produce documents or appear before it in a hearing.
"At this stage, the royal commission is focused on considering written evidence," Mr Hanger said in a statement.
The commission set up by the Abbott government is investigating whether the Rudd government was warned about the dangers of the scheme.
Labor workplace relations spokesman Brendan O'Connor said that while it was unusual for the likes of Mr Rudd and Ms Gillard to be summonsed, he was sure all Labor figures contacted would co-operate with the inquiry.
"As always, you wonder whether there is a political motivation behind the government doing this," Mr O'Connor told Sky News.
"I just hope it is not just a political show trial."
It is understood former ministers Lindsay Tanner, Peter Garrett, Penny Wong, Greg Combet, Mark Arbib and Wayne Swan have been contacted by the commission and shadow attorney general Mark Dreyfus is providing advice.
Former Liberal Prime Minister Malcolm Fraser questioned moves to summons Mr Rudd and Ms Gillard, which breaks the political convention that governments not hold such inquiries into their predecessors.
"Former prime ministers subpoenaed by royal commission. Bad practice," he tweeted.
Matthew Fuller, Rueben Barnes, Mitchell Sweeney and Marcus Wilson all died while working on the $2.8 billion "pink batts" program established by the Rudd government in early 2009.
The men's families have blamed the rushed rollout of the program and lax standards for the deaths.
The inquiry report is expected by the end of June.
