Federal Treasurer Wayne Swan was hardly surprised that Fortescue Metals Group (FMG) launched a legal challenge on Friday that questions the constitutionality of the Gillard Government-initiated minerals resource rent tax (MRRT) set to take effect in July.

A statement by the office of Mr Swan, who acts as the country's temporary chief while Prime Minister Julia Gillard is out of the country, said that FMG owner Andrew Forrest has made its clear in the past that he was "staunchly opposed to the government spreading the benefits of the mining boom to millions of households and small businesses who aren't in the fast lane."

His latest move was not a disturbance at all, Mr Swan said, as he reiterated the federal government's commitment to get on with the 30 per cent tax that will be exclusively levied on coal and iron ore miners operating in Australia.

With a projected haul of more than $9 billion over the next three years, Mr Swan said that he is more than determined to "deliver the MRRT to ensure the Australian community shares in the benefits and opportunities of the mining boom."

"The Gillard government believes Australia's non-renewable natural resources belong to all Australians, not just to a handful of mining billionaires," the treasurer added in his statement.

Fortescue confirmed this morning of its legal action against the mining tax, with FMG chief executive Nev Power stating in a filing before the ASX that its decision was backed by solid legal opinions.

"We believe we have a good case for challenging the Minerals Resources Rent Tax on constitutional grounds and we look forward to the resolution of these important issues in the High Court," Mr Power said in the statement.

The main meats of FMG's arguments against the MRRT are its provisions' tendency to overlook a state's sovereignty and the unusual preference that the tax extends to specific states, Mr Power said.

This early, FMG found an ally on the Coalition, which called the looming legal battle over the controversial MRRT as inevitable.

"The mining tax is a bad tax negotiated personally by (Prime Minister) Julia Gillard and Wayne Swan through a highly improper process," The Herald Sun reported Opposition assistant treasury spokesman Mathias Cormann as saying in a statement.

Senator Cormann reiterated the Coalition's accusations that the MRRT was the result of the concession given to three mining giants, namely BHP Billiton, Rio Tinto and Xstrata, by the Labor-led government, which in turn had left out smaller mining firms and even state governments.

His assertion was backed by Western Australia Premier Colin Barnett, who said today that he "would consider participating in the High Court challenge by way of intervention."

"This is in order to try to protect the ownership of the assets of the state-owned natural resources of West Australians," Mr Barnett said in a statement.