The Maori Party is expected to give the final go-ahead to the Emissions Trading Scheme today - with the price of its support expected to include a $50 million forestry deal for five iwi.

A press conference is scheduled today for Prime Minister John Key, Climate Change Minister Nick Smith and the Maori Party co-leaders to sign off on the scheme after weeks of negotiations.

Full details are secret, but the deal is understood to give five iwi rights to plant trees on conservation land and take profits from the carbon credits.

Te Runanga o Ngai Tahu chairman Mark Solomon is reported to have announced that the deal was worth $50 million a year at the iwi's annual meeting at the weekend.

Mr Solomon - who is also on the Iwi Leadership Group - could not be contacted yesterday, but Labour MP Charles Chauvel said Mr Solomon had said it was worth $50 million a year to the iwi.

The plan to give Ngai Tahu, Waikato Tainui, Te Uri O Hau, Ngati Awa and Ngati Tuwharetoa rights to plant conservation land follows their claims that they were not fully informed about the impact any scheme would have on forestry land purchased as part of Treaty of Waitangi settlements.

The scheme will punish foresters who fell forests planted before 1990 to convert the land for other uses. The five iwi had planned to take the matter to court and the deal will prevent that.

But the proposal was criticised last week as Labour sought to secure more details from the Government, claiming it was negotiating "dirty" deals which gave iwi preferential treatment over others in the forestry industry.

Yesterday Dr Smith refused to confirm the reports that the deal was worth $50 million, saying only that it was worth significantly less than the estimated liability to the Crown of between $78 million and $130 million if the iwi won in court.

He said the deal was not yet finalised and would not confirm when an announcement would be made. But both National and Maori Party sources confirmed a press conference today, just hours before Maori co-leader Tariana Turia goes to hospital for a stomach-stapling operation.

Last week National gave notice Parliament would be going into urgency this week, when it is expected to put the bill through its final stages.

The Cabinet and the Maori Party caucus are expected to sign off the final details before the press conference. The Maori Party had given National a list of 10 requests, all of which Dr Smith had said he was confident could be met.

The Maori Party also sought an extension to the home insulation scheme, more iwi involvement in joint ventures, incentives for further tree-planting, especially of indigenous forests, and more support for green technology.

The deal means the Emissions Trading Scheme introduced by Labour last year will be ditched and replaced by National's, which gives large emitting industries such as agriculture a much longer period before they become fully liable for their emissions.

Giving support to the scheme is a controversial move by the Maori Party, which until recently opposed any emissions trading scheme and was concerned about offloading costs on to low-income families. It began to negotiate after lobbying from Maori businesses.