The High Court has reserved its decision on whether to strike out new New South Wales laws which shore up the powers of the NSW corruption watchdog.

The laws were introduced by the NSW Government after a High Court ruling in favour of NSW crown prosecutor Margaret Cunneen earlier this year.

In the new case before the High Court, NSW miner Travers Duncan, who is a large shareholder in Cascade Coal, is trying to have a corruption ruling against him by the NSW Independent Commission Against Corruption (ICAC) over a Hunter Valley mining tenement overturned.

The ICAC found Mr Duncan engaged in corrupt conduct by concealing the involvement of the Obeid family in the tenement.

Today Mr Duncan told the High Court the new NSW laws were unconstitutional, as they oust the power of the Supreme Court over ICAC actions, which means that the NSW Parliament is effectively directing an independent court.

But the ICAC argued the new law does not direct the courts, it simply changes the law to be applied by the courts.

In the Cunneen case, the High Court found the ICAC had no power to investigate allegations against the well-known prosecutor.

The commission took the case to the High Court claiming a NSW Court of Appeal ruling in Ms Cunneen's favour had taken too narrow a view of the definition of corruption.

Ms Cunneen always denied allegations she advised her son's girlfriend to pretend to have chest pains after an accident to avoid a breath test.

The case has now been dropped completely.

But the High Court case established an important point about the definition of corruption in the ICAC Act.

In its judgment the court found that to be corrupt, an action would have to, or could, adversely affect the probability, as opposed to the efficacy, of the exercise of a public official.

That distinction meant many of the ICAC's past rulings may have been compromised.

The new law seeks to address the problem.

New laws do not reverse High Court decision: Baird

Introducing the new law, Premier Mike Baird said the bill did not reverse the High Court's decision.

"It validates actions and findings of the ICAC before April 14, 2015 where they were based on the previous understanding of the ICAC's jurisdiction," he said.

Four other states have lined up to support New South Wales in arguing the new law does not involve a direction from the Parliament to the courts, and is not unconstitutional.

It is the fourth ICAC case to come before the High Court this year.

Apart from the Cunneen case, Mr Duncan lost an earlier bid to overturn a separate law, which stripped him and others of mining exploration licences.

The court is also still considering another case, in which former Newcastle mayor and developer Jeff McCloy is challenging the New South Wales ban on developers making political donations.