The heat goes on for the debacle on Australia's controversial 30 per cent minerals resource rent tax as small- and mid-sized Australian mining company executives denounced the proposed mining law as putting smaller mining firms at most risk.

Treasurer Wayne Swan immediately rejected the claims before Parliament Thursday and said most of the revenue collected will come from large miners.

The group of small- and mid-sized Australian miners present during the deliberation, led by Fortescue Metals Group Ltd. founder Andrew Forrest, BC Iron managing director Mike Young and Atlas Iron chief Dave Flanagan, stressed the big mining companies will not pay the new tax. The group further warned the tax will stifle Australia's economic competitiveness and business relationships.

Using projections released by accounting firm DBO, the group said the tax would impose on small- and mid-tier miners an effective rate of 46 per cent, while BHP Billiton and Rio Tinto would pay no tax due to large deductions.

Moreover, the bigger mining houses would pay no tax under the plans for up to 25 years.

"The government hasn't thought this through," Forrest told reporters present during the Parliament deliberations.

But Swan lambasted Forrest, who portrays himself as a small miner.

"He's got an A$20 billion company. An A$20 billion company isn't a small miner," Swan said.

"The truth is they don't want to pay any tax," and don't want the Australian people to get a fair return, Swan said on Fox News.

At least 10 bills will be introduced by government to enable the setting up of the MRRT. The MRRT aims to tax the extraordinary profits of coal and iron ore miners from July 2012. The Gillard government had been adamant in explaining that those expected to pay the biggest MRRT are the most profitables.

Apart from the MRRT, debate on the Petroleum Resource Rent Tax Assessment Amendment also gets introduced in the lower house Wednesday. The draft Petroleum Resource Rent Tax Assessment Amendment aims to extend the tax to all oil and gas projects. Nine other related bills are also up for debate.

The entire package will be referred to the House of Representatives economics committee, which will submit a report to Parliament by Nov. 21. The government hopes the bills get passed by year's end.