The ICAC says the four-to-one majority decision of the court imperils some of its most high-profile investigations as well as past convictions flowing from some of its inquiries.

Mr Carr said the people of NSW "want a strong ICAC that has got robust powers when it comes to investigating corruption of the governmental political process".

"I think we're all looking to both sides of politics to shake this judgment out and work out what amendments are required," he said.

"Everything should be considered, even including the prospect of fixing it up retrospectively, if that is required for ICAC to proceed with the cases that have generated the headlines."

The ICAC has urged Premier Mike Baird to consider retrospective laws to reverse the High Court decision, which found that the watchdog did not have the power to investigate Crown prosecutor Margaret Cunneen, SC.

The commission warned that the decision would "severely restrict" its ability to report on recent inquiries into Obeid-linked company Australian Water Holdings and Liberal Party fundraising.

Mr Baird said on Tuesday that he would meet ICAC Commissioner Megan Latham when she returned from leave on April 27.

He said the government wanted a "strong ICAC" but it would "consider this with a cool head".

The ICAC has long operated on the basis that it could investigate allegations that a private citizen misled a public official in a way that could have led to a different outcome.

A 2005 review of the ICAC Act, conducted by Bruce McClintock, SC, recommended the Carr government consider a minor amendment to the laws to clarify its power to investigate such cases, which it termed "indirect corruption".

Mr McClintock said that had the amendment had been made, "there can be no doubt that ICAC would have been entitled to investigate the allegation against Margaret Cunneen and the result of the case would have been different".

Asked if he had concerns about the ICAC's powers while premier, Mr Carr said: "I can't remember it ever coming up as a concern."

Mr McClintock did not comment on the desirability of changing the act now, saying there was force in the arguments on both sides.

But he did say: "My personal opinion is that ICAC should not have commenced the Cunneen investigation."

He said this had "nothing to do with the question of power" but there was a separate requirement - inserted in the ICAC Act on his recommendation - that the commission focus "as far as practicable" on serious or systemic corruption.

"There is no way that what was alleged against Margaret could satisfy that test of serious and systemic corruption, and so ICAC should not have taken up the reference," he said.

"If there were evidence of the commission of a criminal offence, it should have been left to [the NSW police]."