The New South Wales Attorney-General has become a defendant in a court case that is trying to shut down a corruption inquiry into coal licences.

In an unusual move, mining magnate Travers Duncan is trying to shut down an inquiry into the Mount Penny coal licence and stop the Independent Commission Against Corruption (ICAC) making any findings on the grounds of bias towards the NSW Government.

The three-month public inquiry Operation Jasper has finished, but the ICAC is still taking written submissions and is yet to hand down its findings.

Mr Duncan is one of seven investors whose company Cascade Coal allegedly won a rigged tender that covered Upper Hunter properties owned by former NSW Labor minister Eddie Obeid and his associates.

During a hearing of the case, the Supreme Court was told the Attorney-General had become the third defendant along with the ICAC and its commissioner, David Ipp.

The public gallery was full for the hearing and people were also standing in the corridor outside to try to hear what was being said in court.

Mr Duncan's barrister, Noel Hutley SC, accused Mr Ipp of "exciting media interest in the case" by mentioning at the public inquiry that he had received a letter from Premier Barry O'Farrell asking for advice about coal exploration licences.

Mr Hutley accused Mr Ipp of not painting the full picture, saying he had liaised with the State Government over the licences about a week before the letter was read out.

Mr Hutley said while the letter seemed to be a "bolt from the blue", Mr Ipp had himself approached the Premier's Department but failed to disclose the fact.

Mr Hutley said media reports about the letter were incorrect and could influence public opinion and he raised certain issues about planning laws.

Mr Ipp's barrister, Brett Walker SC, said his client had shown no bias and had no "undisclosed dealings" with the Government.

Mr Walker said the ICAC was not like a court and that Mr Ipp had only ever given the impression he would make findings after fairly considering all the evidence.

Mr Ipp will hand down his findings into Operation Jasper and into Operation Acacia, a separate coal inquiry which is currently underway, in July.