The High Court has thrown out a challenge to Labor's mining profits tax but it could be a short reprieve for the controversial measure.
The coalition plans to abolish the Minerals Resource Rent Tax (MRRT) if elected.
"The mining tax will be gone as of July 1 next year if you vote for the coalition," Opposition leader Tony Abbott vowed on the campaign trail in Adelaide.
The legal challenge against the tax was launched by Fortescue Metals Group and four subsidiaries, backed by big mining states Western Australia and Queensland.
Fortescue, which hasn't paid any MRRT and doesn't expect to for years, argued the tax differed in each state because of varying rates of state royalties, contravening constitutional requirements that taxes be levied uniformly across the nation.
But High Court judges unanimously disagreed.
The Labor government said the MRRT was constitutionally sound.
"It ensures Australians will receive a fair return from the nation's iron ore and coal resources into the future," Treasurer Chris Bowen and Attorney-General Mark Dreyfus said.
The MRRT operated in the same manner as the quarter-century old Petroleum Resource Rent Tax which had raised more than $28 billion, Mr Bowen and Mr Dreyfus said.
"By contrast, Tony Abbott wants to hand out a tax break to mining companies and pay for it by ripping away tax cuts for small businesses and making $70 billion in budget cuts."
Fortescue, which must pay the costs of the case, was disappointed.
Chief executive Nev Power said Fortescue had challenged the MRRT because it was an unreasonable intrusion into state responsibilities, also unfair, discriminatory and complex.
The mining industry already paid more tax, including company tax and state royalties, than any other sector, with Fortescue expecting to pay $1.5 billion in 2013-14 and $2 billion in coming years.
He said objections to the MRRT were borne out by the small amount of revenue collected by the tax.
It produced just $200 million in its first year and $700 million in the second - well down on forecasts.
Mr Power wants the coalition to scrap the MRRT, as does Queensland Attorney General Jarrod Bleijie who described it as a failed cash grab.
"It was important to intervene in the case because we could not sit back and let the federal government indiscriminately tax the people of Queensland," he told AAP.
"Mining is one of the four pillars of the Queensland economy."
Australian Greens leader Christine Milne said the government should change the tax so it raises more money.
"It is flawed. It's not raising any money. Rio Tinto didn't pay any in the June quarter. How ridiculous is that?"
