CANBERRA -- Some of Australia's biggest corporate names, including resource giants Rio Tinto and Woodside, may be investigated by consumer regulators over complaints they have been deceptive on climate change.

The Australian Conservation Foundation (ACF) asked competition regulator the Australian Competition and Consumer Commission (ACCC) to investigate whether six companies had been misleading in public statements on the impact of climate policies to gain extra compensation from the centre-left government.

As well as Rio and Woodside, companies named in the complaint included London-listed coal miner Xstrata, Australia's top building products maker Boral, oil refiner Caltex Australia and BlueScope Steel, the country's largest steelmaker.

"Some of Australia's biggest corporate polluters appear to be presenting the worst case to government and the public in an effort to gain excessive free permits, while presenting the best case to investors, in order to keep their share prices up," ACF Executive Director Don Henry said on Monday in a statement.

The ACF has estimated Australia's six heaviest polluting industries will gain at least A$1.1 billion ($896 million) in added compensation under recent changes to the government's planned emissions trading scheme, currently before parliament. The scheme, beginning in 2011 and aimed at reshaping the A$1.1 trillion economy to slash carbon emissions, is set for upper house Senate defeat over the next fortnight.

The ACF, opposing corporate demands for greater compensation, said free emission permits for big polluters meant the government would be handing over A$16.4 billion in compensation, with A$11.7 billion going to just 20 firms.

An ACCC spokeswoman said a decision on whether to accept the complaint had not been made yet. But under sections of the Act covering misleading behaviour, the ACCC can ask companies to accept legally enforceable undertakings to correct breaches.

Authorities in Victoria state, meanwhile, said they were taking seriously threats of violence against the Chief Executive of the Hazelwood coal-fired power station as debate intensified on the government's carbon emissions scheme.

The militant Earth Liberation Front could not be taken lightly with US authorities ranking them as a security threat, Victorian Energy and Resources Minister Peter Batchelor said.

Two upper house Senate committees were to hand over reports on the carbon trading laws on Monday with no sign the government will get its plan through the upper house by the end of next week, when parliament rises for the long winter break.