Drawing the battle lines in its dispute with Ms Cunneen SC, the Independent Commission Against Corruption says in written submissions that it is of "public importance" for the court to "resolve authoritatively" the scope of its investigative powers.

The commission says the ruling by a 2-1 majority of the NSW Court of Appeal that it was acting outside its powers in investigating Ms Cunneen has "potential implications for at least three current investigations", which are shrouded in secrecy.

The ruling affects the ability of the commission to investigate private citizens over their dealings with public officials and the ICAC believes the interpretation of its powers by the majority judges is too narrow.

The commission says corruption findings made against 26 people between June 2010 and the present may need to be reconsidered unless the High Court overturns the decision.

Businessmen who were found to have acted corruptly by concealing the Obeid family's interest in a coal tenement, including mining mogul Travers Duncan, are expected to rely on the Cunneen decision as part of their Court of Appeal challenge to those findings.

The ICAC has deferred releasing its reports in high-profile inquiries into Obeid-linked company Australian Water Holdings and Liberal Party donations until the Cunneen case is resolved. It says the majority ruling has created "uncertainty" about whether it had the power to investigate all the allegations in those inquiries.

At the centre of the ICAC investigation into Ms Cunneen is the allegation she advised her eldest son Stephen's girlfriend Sophia Tilley to feign chest pains to avoid a police breach test after a car crash. She denies the allegations.

Ms Cunneen lost a Supreme Court case to shut down the investigation but she appealed the decision and in December a majority of the Court of Appeal ruled in her favour.

The state's top judge, Chief Justice Tom Bathurst, dissented and would have allowed the inquiry to go ahead.

The Cunneen case hinges on the meaning of "corrupt conduct" in the 1988 Act which is the source of the ICAC's powers.

The ICAC Act contains more than one definition of corrupt conduct. The Cunneen case is concerned with a definition that applies where the dealings of private citizens - including Ms Cunneen's son and his girlfriend - are being examined.

The ICAC Act defines corrupt conduct involving private citizens as conduct which "could adversely affect" the exercise of a public official's functions. It says the conduct could involve criminal offences including perverting the course of justice.

All three Court of Appeal judges said the alleged conduct in the Cunneen case could amount to perverting the course of justice.

But the majority, Justices John Basten and Julie Ward, said it could not "adversely affect" the exercise of a police officer's functions because there was no suggestion the officer "acted otherwise than honestly and impartially".

The commission says the majority decision will affect its ability to investigate conduct "which could have negatively affected the exercise of public functions" but did not involve dishonesty or impartiality by officials.

This may be the case where a person is alleged to have misled an official to bring about a corrupt result.

The people who may be affected by the decision include former Australian Water chairman Nick Di Girolamo, the Liberal fundraiser who gave former Premier Barry O'Farrell the now-infamous bottle of Grange.

The commission says the majority erred by putting a putting a "gloss" on the text of the ICAC Act.

"Whether one prefers to cite Shakespeare's Juliet and roses, or Lewis Carroll and Humpty Dumpty, if Parliament has provided an exhaustive definition of a term, then it is that definition which identifies what the Parliament means," it says.

This is a reference to the famous quote in Romeo and Juliet that "a rose by any other name would smell as sweet". In Carroll's Through the Looking Glass, Humpty Dumpty tells Alice: "When I use a word, it means just what I choose it to mean."

Ms Cunneen's silk in the Court of Appeal, Arthur Moses, has said "sweeping statements" by the commission about the implications of the decision are "overkill".

The High Court will hear the case in Canberra on March 4.