The federal government's new resources tax regime was hammered out with the big three miners at the expense of others, a lobby for smaller mining companies argues.
The three companies that engaged in talks with the Prime Minister, BHP Billiton, Rio Tinto and Xstrata, have welcomed the reforms, saying they are encouraged by the scrapping of the Resources Super Profit Tax.
The so-called Big Three say the agreement meets the mining industry's core principles that any new tax not be applied retrospectively, so existing projects where investment decisions have already been made are not adversely affected.
However, smaller mining companies are not so upbeat.
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Association of Mining and Exploration Companies chief Simon Bennison said his group was left out of the negotiations.
Small miners would be disadvantaged by the new arrangements announced on Friday, Mr Bennison said.
"The government feels the only way it can negotiate through these sorts of situations is with three companies," he told ABC Radio, referring to BHP Billiton, Rio Tinto and Xstrata.
"That's an absolute nonsense.
"That's not the way to do business. It typifies the way this government responds to small businesses in this country."
Small miners with resource profits below $50 million a year won't be liable to pay the new tax.
The group plans to continue campaigning against the 30 per cent tax, now limited to just 320 companies mining iron ore, coal, oil and gas.
