The Northern Territory government's decision to cut funding to the anti-corruption watchdog will impact on its ability to perform its duties, ICAC boss Michael Riches has warned. 

During last month's budget, the Office of the Independent Commissioner Against Corruption was allocated $5.4 million for the upcoming financial year — $1.3 million less than the previous year.

On Tuesday, Mr Riches told a budget estimates hearing the funding reduction comes at a time when the ICAC is conducting 14 significant investigations, in addition to three other preliminary enquiries.

He said his office is also defending five Supreme Court cases brought against his predecessor, including one matter in which $150,000 has been spent on external lawyers so far.

Despite the funding challenges, he said the government had rejected a recent budget allocation submission he had made.

"I am of course disappointed that that is the case," Mr Riches said.

"The significant reduction from this year's budget will of course impact the discharge of my statutory functions."

Opposition Leader Lia Finocchiaro told the hearing the government's budget cut "doesn't pass the pub test".

"What you have is the government of the day, who are undoubtedly under investigation, then cutting 20 per cent of the budget, knowing that that then impacts service delivery and the ability of the ICAC to undertake those investigations," Ms Finocchiaro said.

Chief Minister Natasha Fyles said the ICAC could apply for a "Treasurer's advance" if it requires additional funding.

"The nature of the work that these types of investigative bodies undertake, does, from time to time, see the need for more expenditure, and we certainly support having an ICAC in the Territory," Ms Fyles told the hearing.

Mr Riches said while he was "very grateful" for the opportunity to seek additional funding, he noted the importance of having experienced investigative staff on a permanent basis.

"Corruption investigators aren't just sitting around waiting to be called [for short-term contracts]," he said.

The budget papers noted this year's reduction in funding was mainly due to the expiration of increased funding provided in the 2020 budget.

'Misleading cabinet' claims unable to be investigated

During Tuesday's hearing, Mr Riches also revealed that legislative restrictions had prevented him from investigating an allegation that cabinet had been misled.

"It's a matter that in my view was quite a serious matter," he said.

"It related to an allegation of misleading cabinet."

The claim was levelled against someone outside of cabinet, but Mr Riches said the ICAC Act prevented him from examining documents given to the decision-making body.

"Because I've not been able to access the Cabinet documents themselves, I simply cannot progress with the investigation because the Cabinet documents themselves are key to the investigation."

Mr Riches said he would provide further comments about the legislative restrictions in a general report he intends to provide to the Parliament soon.

Since Mr Riches became the ICAC boss a year ago, he has only revealed the nature of two of the matters his office is currently investigating.

The first related to the the decision to arrest and charge NT police officer Zachary Rolfe over the fatal shooting of Kumanjayi Walker in 2019.