Mining boss Andrew Forrest says his High Court challenge against the federal government's mining tax is about conquering evil.

All it took for evil to win was for good people to do nothing, the Fortescue Metals Group chairman said.

"We've decided not to do nothing," he told ABC radio this morning.

Fortescue is challenging the legality of the minerals resource rent tax, levied against iron ore and coal miners' super profits.

The 30 per cent tax took effect from July 1.

"Our enthusiasm to run this case is because we believe it's fundamentally unconstitutional," Mr Forrest said, adding that the tax interfered with the rights of states.