The government is arrogant if it thinks it can change the law to push through the Ruataniwha dam project, the Labour Party says.
On Thursday the Supreme Court ruled that the Conservation Minister's attempt to swap protected conservation land for farmland to make way for the dam reservoir was not legally allowed.
The swap would have allowed the scheme to dam 22ha of formerly-protected land and give the Department of Conservation 170ha of nearby farmland in return.
The court ruled the reponsible minister could revoke protected status "only where its intrinsic conservation values no longer warrant such protection", and it was "clear" the protected status of the 22ha was appropriate.
Conservation Minister Maggie Barry said the government would now consider legislating to ensure such land swaps could go ahead.
She said the government had long believed that under the Conservation Act it was allowed to swap a low value piece of conservation land for a piece of land with higher conservation values.
The Labour Party wants the government to confirm whether any legislation to force swaps of conservation land would be retrospective or not.
Environment spokesperson David Parker said it would be constitutionally outrageous if the government sought to overturn the court's decision.
However, Ms Barry said any change will not apply retrospectively, so would not affect the Ruataniwha Dam decision.
Labour's Ikaroa-Rāwhiti MP Meka Whaitiri said the conservation land being swapped for the irrigation scheme was not low quality.
"It's a beautiful pristine area, looking down the valley, so giving that up for another piece of land ... everybody knows it's really swapping land so this dam could go ahead."
Ms Whaitiri said it would be arrogant for the government to legislate to overturn the court's ruling.
"That says a lot about the National government's arrogance and out of touch with pushing through something that clearly people have had a lot of concerns about."
Green Party conservation spokesperson Mojo Mathers said the government wanted to destroy protected conservation land for its private developer mates.
She said it should just respect the court's decision.
Ms Barry dismissed the accusation as "typical of this time of the electoral cycle".
She said DOC held conservation values paramount and was experienced in assessing land swaps with the aim of keeping varied ecosystems and habitats.
Ms Barry said the 170ha of farmland the department would have received had important wetland and forest habitat, and the Director General of Conservation believed the swap was a good conservation outcome.
"The evaluation of DOC on these things is usually spot on, they know what they're doing, " she told Morning Report.
"Ultimately, DOC's core business is doing a couple of these land swaps a year."
Over the past three decades years there had been about two swaps a year, she said.
However "business as usual" for the past 30 years was having to be re-evaluated in light of the Supreme Court ruling.
Ms Barry said she did not know whether any other land swap would now be challenged.
She said when DOC was established it had inherited some "pretty rubbish" land, but its high-conservation-value land would never be touched.