Fortescue Metals Group boss Andrew Forrest on Thursday joined junior mining representatives threatening to launch a new advertising campaign against the Australian government's mining tax.

Shortly after she came to office, Prime Minister Julia Gillard negotiated with mining giants BHP Billiton, Rio Tinto and Xstrata to change the controversial resources super profits tax.

The new scheme taxes profits on iron ore and coal above a 12 percent threshold at 30 percent, but Forrest and other junior mining representatives believe it unfairly hits smaller companies.

Forrest noted many of the details of the deal remain secret and cannot be modeled by his company and other junior miners.

Representative body AMEC (The Association of Mining and Exploration Companies) is considering a new advertising campaign on behalf of the smaller miners, and it could start as early as the weekend.

The miners are also concerned about the preference deal struck between the government and the Greens for the coming election because the Greens have signaled their intention to claw back more money from the miners.

Forrest said Greens Leader Bob Brown knows how damaging the tax will be to the industry, but is supporting it anyway because it will get him votes.

He added the industry invests heavily in Aboriginal employment and training, which will stop if the industry falters.