BHP also lodged full-page advertisements in national newspapers on Friday opposing the tax, and again staking out early opposition to any proposal to shift the RSPT to something closer to the offshore petroleum tax model.

In his letter to shareholders Nasser again criticised the government’s consultation process, contrasting it unfavourably with the Hawke and Keating-led changes to the petroleum taxation system in the 1980s.

In an information package accompanying the letter, BHP pointed out that the then Labor government released three papers for public and industry comment before publicly committing to the tax, which was then enacted over three years, with existing projects largely exempt from the new regime.

In contrast, the current government sat on the Henry Tax Review for a considerable period and announced its support for the RSPT in tandem with the release of the report itself.

Nasser says in the letter that the RSPT needs “fundamental redesign” and that BHP will not support any shift to the PRRT model.

Speculation has grown in recent days that the government will offer some concessions to the industry along those lines, moving the underlying rate from the long-term bond rate of around 6% to something closer to 11% or 12%, and dropping the 40% underwriting tax credit guarantee for project losses.

But Nasser said importing the PRRT model would not work in the mining industry, arguing the shift would not address most of the fundamental issues BHP had with the design of the tax – particularly in that it would still be applied to existing projects, rather than just new projects.

BHP said minerals and petroleum projects were treated under separate tax regimes around the world.

Nasser again said the company was not opposed to tax changes, but that tax reform needed to be “principled” – increased tax rates should only apply to new investment, not existing projects; the overall tax rate should not make the Australian industry less competitive internationally; different minerals should be taxed at different rates to reflect their respective profitability; and any new tax should apply only to the actual minerals and not to infrastructure, downstream processing, manufacturing and transport.

The move comes after BHP chief executive Marius Kloppers took steps to hose down criticism the company is taking political sides, saying it is not aligning itself with the federal coalition in the debate over Australia’s future taxation system.

Kloppers reportedly told journalists yesterday the company was focused on “playing the issue and not the man”