The number of appeals against deportation by non-residents has risen 59 percent following a crackdown on foreign-born criminals.
The Immigration and Protection Tribunal last year dealt with the highest number of appeals in its history. Its annual report said it urgently needed to add to its 16.4 full-time equivalent staff and improve resources.
The report showed it managed to reduce the number of appeals waiting to be heard despite an overall 30 percent rise in cases being lodged and more lengthy refugee and investor category appeals.
It said its chairman last year concluded almost 300 cases - nearly a quarter of the tribunal's appeals - and that workload was not sustainable.
"The tribunal reduced the time taken, from date of lodgement, for disposable appeals to be finalised by a record 36 percent. Appellants are now waiting an average of 56 days less to receive the outcome of their appeal than at the start of the court year," the annual report said.
"The work pressure on the tribunal has also highlighted the urgent need for the Ministry of Justice to develop terms and conditions for tribunal members, so that legitimate expectations can be clarified for the benefit of the members and the ministry."
The report revealed that a confidential counselling service was made available to members from last November for work-related issues due to the intense and stressful nature of some of its work.
It also said the tribunal ability to function effectively was being undermined by the ongoing problems affecting its database of published decisions, which is the primary reference point for tribunal members.
"This year, the tribunal's database has suffered significant problems, with the search engine failing to function properly and the ministry lacking resources to cope with the uploading of the tribunal's decisions," it added.
"These problems remain unresolved, and, at present, uploading of the tribunal's decisions is some six months behind. These issues seriously affect the quality of the tribunal's work and its public service, and it is hoped that the coming year will see them resolved as a matter of urgency."
It said more resources would now be directed at hearing appeals against deportation by non-residents to help address their growing numbers.
The report said the increase in the volume of new appeals appeared to be associated with recent changes in the application of immigration policies.
Two years ago, the Law Society said Immigration New Zealand had been slow to issue deportation liability notices to visa holders who were convicted of a crime but that was now changing.
Of the decisions released in the past year 64.7 percent of appeals were declined, 29.6 percent of appeals were allowed, and 5.7 per cent - all residence appeals - were referred to the Minister of Immigration as special circumstances were identified despite Immigration New Zealand's decision being correct.
The lowest percentage of successful appeals were in the deportation (non-resident) stream where a quarter or 103 cases were approved.