The Corrective Services employee was working in the control room monitor post doing the 6pm to 6am "N" watch at the state's newest jail for 400 inmates, and was still on a six month probation.

He was sacked nine months later, four days before Christmas in 2018, after an investigation found him guilty of misconduct for allegedly sleeping on the job.

In the NSW Industrial Relations Commission this week he fought off a Department of Justice Correctives Services attempt to stop a full hearing of his appeal against the termination later this year.

Commissioner Nichola Constant rejected Corrective Services' argument that it "fairly and squarely" advised him in a letter in June, 2018 that his transition from probation to permanent after six months was on the line because of the alleged sleeping incident.

Instead he was paid and continued working beyond the six-month probation, and in the absence of specific advice from Corrective Services that the probation had been extended, he was a permanent employee when he was sacked, Commissioner Constant found.

She rejected Corrective Services' argument that she had no jurisdiction to hear Mr Wilson's appeal because he wasn't a permanent employee, and ordered a full hearing before September.

The commission was told Mr Wilson was first employed by the department as a casual correctional officer in July, 2016 and was offered a six-month probation in December, 2017 to start full-time work at the new rapid-build Hunter Correctional Centre, which opened in late January, 2018.

The innovative maximum security prison for 400 inmates has no traditional cells and holds 25 prisoners in each of 16 "pods" or open-plan dormitories, where each man has an individual unit.

The commission was told Mr Wilson denied the sleeping allegation in a Public Service Association letter on his behalf to Corrective Services in July, 2018. In August, 2018 Mr Wilson was shown CCTV footage of himself in the control room on March 24, 2018.

Hunter Correctional Centre Governor Richard Heycock advised Mr Wilson that his progression from probation to permanent could not be confirmed until the misconduct process was finalised and a decision made.

Commissioner Constant found there was no provision in the Government Sector Employment Act or Rules that allowed Corrective Services to decide the probation period was ongoing beyond the six months.

The letter to Mr Wilson advising him of the misconduct investigation "does not, on its face, extend the probation period, nor does it explicitly inform (Mr Wilson) that his employment may not be confirmed at the end of his probation period".

"In fact the letter makes no mention of the probation period," Commissioner Constant found.

She dismissed the Corrective Services application to have Mr Wilson's case struck off.

Mediation between the two parties in February, 2019 failed.