FTSE 100 companies Rio Tinto (RIO.L) and International Power (IPR.L) have voiced concerns over the Australian government's proposed climate change plan.

International Power released a statement saying that it would ask the government to consider a voluntary 'contract for closure' for its Hazlewood plant.

The Australian government is seeking to introduce legislation that would bring its carbon dioxide emission to 5 per cent below 2000 levels by 2020.

The plan would see brown-coal fired power generation - such as the Hazlewood plant - be eligible for carbon credits in the first five years from July 2012.

International Power estimate this would result in a shorter asset life for brown coal-fired generation, which in itself represents 5 per cent of its global (net) generating portfolio.

The company believes a contract for closure could provide more certainty and reduce the overall impact of the legislation on the business.

The Australian government's plans to introduce a tax that levied on carbon dioxide emissions of AU$23 (£15) per tonne from 2012 has also been criticised.

Rio Tinto, meanwhile, warned that a carbon tax would affect export industries, investment and job growth, adding that it was 'disappointed' by the news.

David Peever, managing director of Australia for Rio Tinto, said a tax was 'unfair' on exporters.

He said, 'We are deeply concerned the proposed carbon tax fails to shield Australia's export sector and leaves it at a disadvantage compared to international competitors.

'It is crucial that Australia's contribution to the global effort is in proportion to action being taken by overseas trading rivals so as not to disadvantage important trade-exposed industries.'

Peever added, 'We have to be careful about imposing policy experiments on the Australian economy.

'Australia's minerals sector now faces significant additional costs not faced by competitors. This will inevitably reduce potential investment and jobs growth in Australia, without reducing global emissions.'

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