Twenty economists were ridiculed by the Federal Opposition for expressing their support through an open letter on the federal government's proposed resource super profits tax.

A group of well-known economists supported the tax, stating that claims on increasing the cost of living while slowing the growth in the sector are without substance.

However, Ian Macfarlane, the opposition resource spokesperson brushed off the group's statements regarding the tax.

"I think economists are put here to make weather forecasters look good," he said.

Opposition finance representative Andrew Robb said the economists are arguing on the wrong issue.

“The debate is all about the size of the tax grab. The economists are attempting to shift the focus."

Meanwhile, opposition Leader Tony Abbot said in a local radio interview that mining companies are paying more than their fare share of tax once the government adds in corporate taxes and royalties, which is too much.

However, Treasurer Wayne Swan rebuts Mr. Abbot's statements, saying that miners admit they are not paying too much tax.

"That just shows how far Mr. Abbot is out there, with people like [mining magnate Clive Palmer] arguing in the commercial interest of some miners and not arguing in the national interest."

Mr. Macfarlane believes that miners are paying an amount of tax but the proposed tax needs revisions and more detailed consultations from the sector.