Greens deliver ultimatum in upper house for government to release business case for new Dungowan Dam near Tamworth

But, the water minister has slammed the latest move as a political stunt.

The leader of the government in the upper house, Damien Tudehope, was censured over the government's "non-compliance" with an order to release the dam documents after a motion moved by Greens MP Cate Faehrmann.

She told the Leader public interest was at the heart of six requests made in the upper house in the past 12 months to make the business case public.

"The government is hiding behind this overused cabinet in confidence argument to, I think, hide what will be a business case that shows that Dungowan Dam just doesn't stack up," she said.

"I truly believe that these business cases will show that this is an appalling investment decision for the NSW government to make.

"Show us the evidence that you are making a good decision here."

The government was given a week to reveal the business case or finance minister Mr Tudehope will be held in contempt, meaning there'll be a "black mark" against his name, Ms Faehrmann said.

The project had blown out to about $1.3 billion - almost triple the original budget - but the cost-benefit ratio, water price and who would receive allocations from the 22-gigalitre dam are secret.

Ms Faehrmann said the government needed to be transparent and slammed the "excuse" that the documents contained sensitive information as "rubbish".

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"The government is making the false claim that releasing these documents would reveal the deliberations of cabinet. This is simply not the case," she said.

Tamworth MP and Water Minister Kevin Anderson said in a statement the Greens did not represent the interests of the community, didn't live locally and were opposed to dams.

"They weren't here when Lake Keepit was almost empty and Chaffey Dam was dangerously low," he said.

"They don't know the first thing about water security in Tamworth and the Peel Valley."

He argued the Greens had long known cabinet documents cannot be made public due to commercial and cabinet in confidence.

He said the environmental impact statement contained elements of the final business case and would go on public exhibition.

Tuesday's state budget raised concerns Dungowan Dam could be dead in the water after it was confirmed the state contribution of 50 per cent was contingent on the federal government coughing up $675 million.

Member for New England Barnaby Joyce said people would flood out of Tamworth if the project was abandoned.

He said he had plans to meet with the Environment Minister Tanya Plibersek.

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