Corrections Minister Judith Collins has welcomed an Employment Court judgment in favour of the Department of Corrections over plans to extend the use of double-bunking at prisons.

The case was brought by the Corrections Association of New Zealand. It challenged the Department's plans to address a looming capacity crisis by increasing the number of double-bunked cells at four of the country's newest prisons.

"Due to a lack of planning by the previous Government, our prisons are forecast to run out of baseline beds around February next year. We have been in a race against time to ensure there are enough beds to accommodate the forecast numbers of prisoners," Ms Collins said.

"Double-bunking is the fastest way to add extra beds in our prisons. I welcome today's judgment by the Employment Court as it will enable Corrections to manage additional prisoners safely and securely."

The Court found that Corrections' plans to double-bunk at four prisons was not in breach of the union's collective agreement, and that Corrections had met its consultation obligations under the agreement.

Furthermore, the Court found that Corrections' actions had not been in bad faith over the extent of forecast prisoner numbers or the design capacity of some cells, as contended by the union.

Corrections already uses double-bunking at a number of its prison sites and the practice is common internationally - including Australia, Canada, the US and Britain.

To ensure the safety of staff, current prisoners-to-staff ratios will be maintained in prisons with double-bunking, an assessment programme will be undertaken to ensure prisoners are compatible for cell sharing, and Corrections staff will be given extra de-escalation training.