The warning, from the Legislative Assembly's ethics and integrity adviser Stephen Skehill, comes as the select committee examines two different versions of a bill to establish the new commission, from the government and opposition.

While Mr Skehill's evidence on the issue aligns with similar comments made by former judge Stephen Charles, the ACT Bar Association on Monday indicated it was less worried about the issue.

It was one of several issues examined during the hearing, including the qualifications needed for the commissioner, parliamentary privilege and the role of the commission in ensuring its investigations did not potentially affect the ability to prosecute matters arising from a corruption probe.

Mr Skehill told a hearing on Monday he was concerned a lawyer advising a potential witness or subject of a commission investigation would likely advise them to challenge the commissioner's decision to hold a public hearing.

He said that due to a lack of firm criteria enshrined in both the government's exposure draft and the opposition's bill, if such an appeal was made, it could delay or ultimately prevent any public hearing going ahead.

While such an appeal would likely be made public through the courts, if no suppression order was granted by a judge hearing the matter, Mr Skehill said he believed the subject of a corruption investigation would see that as a lesser of two evils compared with a public hearing.

However, immediate past president of the ACT Bar Association Ken Archer said such a view was a very pessimistic view of the legal profession, and that if it was the case, such appeals would be rare and unlikely to take two years.

Mr Archer said he also didn't philosophically see a reason for someone to be picking out one specific part of the process for determining whether to hold public hearings as a reason for an appeal, but the bar association maintained its view the commission's preference should be for private hearings, unless the public interest outweighed that preference.

Other issues canvassed during Monday's hearing included several witnesses including former NSW Auditor-General Tony Harris urging the committee to ensure the commission's budget was set by the Assembly, not the government.

Mr Harris highlighted recent significant budget cuts to the NSW ICAC by that state government, saying the budget should be set by the Assembly to prevent potential ACT government budget cuts hampering its work.

He also urged the committee to recommend putting a new provision in the final bill that would create an offence for not reporting allegations of corruption, again citing cases in NSW where it appeared senior public servants knew of such activity but did not report it for fears it of reprisals that could affect their career.

Several witnesses also urged the committee to recommend widening the proposed qualifications needed for the commissioner, as well as set some for an acting commissioner position, as the current proposals for a judge with at least 10 years legal experience, and basing the position in Canberra, may set the bar too high and lead to few applications.

Mr Archer told the committee that if the current qualifications remained in the final bill, it could mean the only viable candidates would be men aged 70 years or older, while Mr Harris said it could also exclude eminent candidates such as Bret Walker SC, who is currently leading a Royal Commission in South Australia.

Discussions also turned to a provision in the Opposition bill for the Supreme Court to determine if documents sought by the commission may be protected under parliamentary privilege, with witnesses largely urging against such a provision as it could interfere with the separation of powers.

Instead, witnesses including Mr Skehill and Assembly Clerk Tom Duncan urged such an issue instead be decided by an Assembly committee under some yet-to-be-determined agreed set of criteria.

The inquiry is set to wind up next month, with the government planning to introduce and pass a final bill in November.

Clarification: This article has been changed to reflect the bar association's view that the commission's preference should be for private hearings, as the association is not outright against public hearings as previously reported.