The prosecution of four whistleblowers has topped $7.6 million in legal fees.
Attorney-general's department bureaucrats revealed the ongoing prosecution of David McBride has cost the Commonwealth $1,875,000, with $233,000 being spent on the Richard Boyle case as of January 30.
The department said the costs also covered the protection of sensitive evidence.
"We've been seeking appropriate orders in order to protect national security information in the McBride matter," deputy secretary Sarah Chidgey said.
Mr McBride blew the whistle on alleged war crimes in Afghanistan, while Mr Boyle went public with allegations the tax department ordered employees to move towards more aggressive tactics when collecting debts.
The total cost of prosecuting Witness K and lawyer Bernard Collaery - who revealed a bugging operation in East Timor by Australian officials - was over $5.5 million.
The prosecution of Mr Collaery was ultimately dropped on the order of Attorney-General Mark Dreyfus.
Greens senator David Shoebridge called it a "criminally large" amount of money to prosecute whistleblowers.
