The union watchdog has spent more than $1.33 million of taxpayers' money in legal costs linked to raids on Australian Workers' Union offices.
The Registered Organisations Commission is appealing a Federal Court ruling against the regulator's investigation into the AWU.
ROC officials told a Senate estimates hearing on Tuesday that appealing the decision had so far cost $344,000 on top of the $992,000 spent on the original challenge.
Commissioner Mark Bilecki did not rule out taking the case to the High Court if the appeal failed.
ROC officials also told the committee that Labor senator Kimberley Kitching had asked the agency 411 questions on notice since May 29.
ROC executive director Chris Enright said up to 42 per cent of the workforce was working on answering the questions.
Mr Enright said a conservative estimate was that staff spent the equivalent of 115 working days or 867 hours on responding to Senator Kitching in recent months.
Senator Kitching said she asked lots of questions across a wide range of departments and officials.
"Don't think you're anything special. I'm just trying to ensure taxpayers' money is used in the most efficient way it possibly can be," she said.
The ROC has found time to produce a podcast, which Senator Kitching described as a "very expensive undertaking".
One episode of the 10 involved the commissioner, a senior executive, a junior executive and three other public servants.
"That would have been a pretty expensive podcast to produce and you've had 57 listeners," Senator Kitching said.
Mr Enright said the first nine episodes had 1000 downloads in total, but each listener could be representing many others from their union or employer group.
"The feedback we've been getting about those podcasts has been extraordinarily positive," he said.
Labor senator Tony Sheldon questioned the ROC's largesse after confirming Mr Bilecki's annual base salary is almost $350,000.
The commissioner confirmed he also receives extra payments for accommodation for living in Melbourne away from home.
Senator Sheldon said Fair Work Ombudsman Sandra Parker, who earns $388,000, had a similar overall pay package despite having responsible for substantially more employees.
"We've quite clearly not got value for money here," Senator Sheldon said.
Cabinet minister Marise Payne said the comparison was unfair and inappropriate, with pay determined by an independent tribunal.
Australian Associated Press