CANBERRA -

Death threats and electoral backlash against independent MPs crucial to Prime Minister Julia Gillard have underlined the dangerously fragile path that lies ahead of the minority Labor Government.

Pressure on two pivotal New South Wales independents - Tony Windsor and Rob Oakeshott - has mounted since they supported Gillard after last year's election, and has accelerated with plans for a carbon tax.

Nor has Gillard been able to take their support for granted: both opposed the tax levy imposed to help stricken states recover from the summer's devastating floods.

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It passed the House of Representatives with the votes of Greens MP Adam Bandt, West Australian Nationals crossbencher Tony Crook and north Queensland independent Bob Katter.

Crook and Katter are both conservatives more naturally aligned to the Opposition.

And while courting the crossbenchers, Gillard has to balance support from the Greens against the need to maintain a clear distance from them, to avoid constant claims from the Opposition that the Greens are running the Government's agenda.

Most recently, Gillard has had to clearly stamp on demands from the Greens that petrol be included in carbon pricing, a call made well before any detailed work has begun and potentially damaging to a campaign that has already drawn heavy flak.

The carbon tax proposal will test both Gillard's leadership and her ability to haul the independents into her order of battle, even with cracks appearing within the Opposition - notably continued support for emissions trading from former Liberal leader Malcolm Turnbull.

Turnbull has made no secret of his ambitions to again lead the party, adding to recent strains within the Coalition.

But Opposition Leader Tony Abbott is whipping his troops into line while anger grows - and support falls - for Gillard's proposal to introduce carbon pricing from July next year as a transition to an eventual greenhouse emissions trading scheme.

Failure could end Gillard's political career. The issue helped topple former Liberal leaders Turnbull and Brendan Nelson, and was a big factor in the coup that deposed former Labor Prime Minister Kevin Rudd.

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To succeed, Gillard needs to win, and hold, three independents.

She can probably count on Bandt and Oakeshott, but Windsor and Wilkie have yet to be won over, while Crook and Katter are unlikely to be convinced.

For the three independents whose votes Gillard is best placed to win - Oakeshott, Windsor and Wilkie - the merits of the plan that finally emerges will need to be weighed against sentiment in their own electorates and, ultimately, their own political survival.

Recent polling has shown declining belief in human-induced climate change and a lessening of support for action to combat it, a trend echoed in National Party research for this month's NSW election.

Party polling published by the

Daily Telegraph

yesterday said almost two-thirds of state voters were "firmly" opposed to carbon taxation.

Oakeshott, a renegade National who was re-elected last year with a 62 per cent to 37 per cent margin over Nationals rival David Gillespie, has since lost ground in a seat that since its formation in 1952 had previously been held by his old party .

Last September he was forced to cancel a public meeting after a series of threats, and yesterday the

Australian

published confidential Nationals polling showing a collapse in support, to a minus 12 approval rating.

Windsor is also having problems. Another former National, Windsor has maintained strong support since he won the seat of New England in 2001, after more than 90 years of MPs from his former party or its predecessors.

But a poll by Inverell radio station 2NZ, reported in Tamworth's

Northern Daily Leader

, showed overwhelming opposition to a carbon tax.

Windsor has also received death threats, with one message saying: "You're a f***ing liar, a dog, a rat, a big f***ing MP dog ... and you wait you're not going to get voted in again. I hope you die, you bastard."

Windsor yesterday urged cool heads, warning that violent political rhetoric could provoke a similar outrage to the recent shooting of American congresswomen Gabrielle Giffords.

He laid much of the blame on conservative talkback radio hosts, saying is was about using the carbon pricing issue to get some sort of people's revolt to overthrow the Government.