One by one, miners with Australian operations are slamming Canberra's proposed 40 per cent supertax on resource profits. Canberra has dismissed the protests of BHP Billiton, Fortescue Metals, Rio Tinto and Xstrata as huffing and puffing. But miners are upping the ante. Fortescue has already frozen two development projects; now Xstrata has suspended almost A$600m of expenditure on A$6.6bn of coal and copper projects.

Kevin Rudd, the prime minister with an eye on the next election, accuses miners of offshoring profits from Australian mines. It is not as if he needs the tax to repair damage from a deep recession or to slash an embarrassing budget deficit. Yet recent febrile exchanges do little to minimise the upfront damage to an already handsome contributor to tax revenues.

Level-headed, face-to-face consultation from the start would have helped. Miners, after all, concede the need for reform of Australia's convoluted mining tax regime. What rattles them most is the retrospective aspect of the proposed tax, which they argue undermines the viability of existing projects. Alignment with a similar petroleum tax solely on prospective projects might give the government a better argument for implementing the swingeing 40 per cent tax. Miners can hardly relocate to more fiscally benign Canada, for example. Even so, a one-size-fits-all tax would favour BHP Billiton and Rio Tinto, able to achieve juicy margins on iron ore, more than, say, Xstrata with its coal and copper operations.