BHP said any change to tax regulations by The Australian Government must only apply to new projects to ensure minimum impact on the country’s resources industry.

The 40% resource ‘super’ tax proposed by the Australian Government has generated widespread criticism from mining giants including BHP Billiton and Rio Tinto, which have warned they may take projects offshore if the new tax rules are enforced.

“Any reform proposal must only apply to new investments: not to existing investments. Additionally any reform should not disadvantage the resources industry compared to other industries in Australia and it absolutely must not disadvantage the Australian resources industry compared to other countries”, chairman Jac Nasser said in a letter.

Nasser warned the enforcement of such a tax could make Australia a less stable and less competitive place for long-term investment in the mining industry.

In its letter to shareholders, BHP said it has invested $11bn in project development and paid A$6.3bn ($5.5bn) in tax to the Australian Government, the company said.

BHP said it will make a deeper study of the implications before making future investment decisions.

The proposed tax will increase BHP’s tax rate from 43 to 57%, the company said.