Fortescue Metals Group chief executive Nev Power says the iron ore miner expects to launch a constitutional challenge to the Federal Government's mining tax within weeks.
Mr Power said the miner was briefing counsel "as we speak".
"We would expect to be launching that challenge in the next few weeks," he told reporters this morning as Fortescue released its quarterly production results.
Fortescue has made no secret of its plans to head a High Court challenge to the tax, which passed through the Senate with the support of the Greens last month.
They are expected to argue the tax breaches the Federal Constitution because it discriminates between the States and it directly taxes resources owned by the State.
FMG's founder and now non-executive chairman, billionaire Andrew Forrest, has been a vocal opponent of Mineral Resources Rent Tax since it was introduced by Prime Minister Julia Gillard following consultation with the big miners, BHP Billiton, Rio Tinto and Xstrata.
Mr Forrest says the tax unfairly discriminates against the smaller and mid-tier miners, who he claims were locked out of negotiations.