The Federal Government has secured the support of key independents Tony Windsor, Rob Oakeshott and Andrew Wilkie for its mining tax.

The independents have secured a $200 million program to examine environmental concerns over coal seam gas mining and an increase in the tax threshold from $50 million to $75 million for small companies.

But the passage of the bill is by no means assured.

The Greens, who have threatened to block the legislation if the tax threshold is increased, are insisting the foregone revenue of $20 million a year be made up by other means.

However the support of the independents is a big boost to Julia Gillard's Government, which is trying to get the tax through the Lower House before Parliament rises for the year on Thursday.

It has been buoyed by Labor Party-commissioned research showing 56 per cent of people do not think average Australians are benefiting from the resources boom.

The Government has agreed to a demand by Mr Wilkie to lift the tax threshold at which the tax will apply to $75 million from $50 million and phase in another increase to $125 million.

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Mr Wilkie had expressed concerns about how the tax will affect small miners, a concern shared by Western Australian independent Tony Crook.

The Tasmanian MP says 20 to 30 companies will pay the tax when it reaches the $125 million threshold.

"That will go some way to making for a fairer tax for the small mining companies," he said.

"At the end of the day they are the companies that are going to become the big companies."

Mr Wilkie said he was unable to negotiate any change to the depreciation provisions, but accepted the Government had negotiated in good faith.

But Mr Crook says he will not be supporting the tax and argues the Government should consider amendments to protect small miners.

"Some companies may choose to put their projects on the backburner or not proceed at all," he said.

"This will have a massive detrimental affect. There should be every inducement to keep these mining companies going and keeping people employed."

Sticking points

One of Mr Windsor's key sticking points was a commitment that any decisions about coal seam gas projects are based on rigorous scientific evidence.

The Government has agreed to his request.

Greens leader Bob Brown says his party will not budge from its demand that any amendments deliver a revenue-neutral position.

He said it was now up the Government to "get creative" to fund community services that would suffer from the $20 million decrease.

"Twenty million is 200 or 300 nurses or teachers sacked off the payroll. Andrew Wilkie might explain that to the nurses at the Royal Hobart or the teachers at Ogilvie High," Senator Brown told reporters.

"Giving a free $20 million back to the mining industry - and these are corporations turning in a profit of over $100 million a year - isn't something we are going to entertain.

"It's up to them to make this a revenue-neutral arrangement and it's part of a stand we're taking here for average Australians."

Internal friction

Earlier today, Opposition Leader Tony Abbott refused to respond to press reports that some in his party now favour the tax, despite the Coalition’s pledge to repeal the measure if it wins government.

The Sydney Morning Herald quoted an unnamed Liberal MP as saying there is a growing view within the Coalition that the tax will be needed to fund the party's promises.

West Australian Liberal Mal Washer has already publicly supported the tax - but says he will not cross the floor to vote with the Government.

Asked twice about the rumblings within his own party, Mr Abbott this morning would only say "this is a bad tax from a bad government".

After the second question, Mr Abbott told reporters to change the subject.

"I've made it very clear what our position on the mining tax is - if there are other issues we want to deal with today, that's great."