The Australian Greens are looking to a plug a hole in the Federal Government's mining tax that will stop resource companies claiming credits for increased state royalties.
Under the Minerals Resource Rent Tax, companies can offset their liabilities by claiming back royalties they pay to state and territory governments, including any increases from July 1 onwards.
Greens leader Christine Milne will introduce a private bill to the Senate that does away with credits on any increases.
The Parliamentary Budget Office estimates the measure would raise $2.2 billion over the next three years.
"Let's actually plug the gap," Senator Milne told reporters in Canberra this morning.
The Greens still prefer Labor's original 40 per cent resources super profit tax, but supported the MRRT in parliament because it was "an opportunity to raise some money".
The MRRT is forecast to raise $2 billion this financial year, but reports suggest nothing was raised in its first three months of operation.
"The fact that it has raised nothing shows it was badly designed," Senator Milne said, adding there were too many concessions.
"That's why we are trying to fix it."
The Greens argue tax revenue is needed for projects such as Denticare and the Gonski education reforms.
However, Senator Milne would not support calls for a tax review that includes the GST, as suggested by independent MPs Rob Oakeshott and Tony Windsor.
Mr Oakeshott is meeting with Treasury officials in Sydney to discuss the MRRT and state-based royalties to try to "get a handle" on just what revenue has been raised.