National anti-corruption commissioner Paul Brereton is facing calls to resign as he's investigated for potential misconduct.
Mr Brereton is under scrutiny following referrals about potential conflicts of interest due to his prior employment with Defence, and his continued involvement with the department's watchdog.
Inspector of the National Anti-Corruption Commission Gail Furness had opened investigations into "agency maladministration or officer misconduct", she said in a February 6 letter to a parliamentary committee overseeing the commission that was publicly revealed on Monday.
Mr Brereton stirred controversy after he failed to disclose he had continued to provide advice to the Inspector General of the Australian Defence Force on a casual basis after becoming the commissioner.
The major general had consulted with the inspector general on his inquiry into potential Australian war crimes in Afghanistan about 22 times since 2023, he admitted when he last fronted a parliamentary hearing in December.
He has defended his actions, arguing he only provided informal assistance without pay on a matter he was an expert in after his report found credible evidence of potential war crimes involving the killing of 39 Afghans between 2005 and 2016.
Mr Brereton has said he told the then attorney-general he intended to continue to provide advice to the inspector general when he was first appointed in early 2023 due to his expertise in the area.
But subsequent Attorney-General Michelle Rowland wrote to Mr Brereton in October 2025, issuing a please explain, saying he had not adequately disclosed his work with the inspector general.
Ms Furness admitted people had lost confidence in the commissioner.
"There has been expressed to me a reduction in confidence of the commissioner in dealing with defence-related matters because of his not disclosing it to the (commission's) CEO," she told a Senate hearing on Monday.
Further complaints against Mr Brereton include potential conflicts of interest in Defence cases arising from his previous employment.
He recused himself from all defence-related matters in late 2025.
The parliamentary committee deputy chair and independent MP Helen Haines said Mr Brereton had to decide between his job as commissioner and his defence advisory role.
"The inspectors' decision to investigate complaints against Commissioner Brereton is extremely serious," she said.
"Australians are disappointed and concerned that, since the NACC's establishment, so much attention has been on the commissioner himself."
Independent senator David Pocock has called for the commissioner to resign, saying public confidence in the national anti-corruption commission was paramount and Mr Brereton's actions were damaging its reputation.
"We must restore the public's trust in the national anti-corruption commission," he said.
"The commissioner's position is completely untenable and it's time he did the right thing and moved on."
Greens senator David Shoebridge called for the government to sack Mr Brereton, saying the commission needed to be spending time and resources investigating corruption and not defending its commissioner.
"It's time for Labor to read the writing on the wall and work with parliament to remove Commissioner Brereton and then start rebuilding trust in the NACC," he said.
