Senior Labor MP Gary Gray has dismissed the need for exempting magnetite miners from the new mining tax, which Premier Colin Barnett backs.
Speaking in Geraldton he said taxing the magnetite at the mine gate before it was upgraded meant it would never attract any tax.
"This magnetite has such a low value at the mine gate that it's impossible to see that it will be caught in this tax environment," Mr Gray said.
Earlier, Premier Colin Barnett maintained that magnetite must be excluded from the tax, saying the uncertainty threatened 16 magnetite projects worth $40 billion in WA.
He said that exempting magnetite would actually grow the tax by encouraging development.
Mr Barnett said it also made the Oakajee project "a bit more difficult."
"It's a further complication we don't need," Mr Barnett said.
"I've pleaded with the prime minister to take magnetite out of the tax to remove uncertainty.
"If you exclude magnetite, you'll get more (government revenue) by stimulating the sector.
"I expect that this is an oversight and another example of how they (the federal government) don't understand the mining sector."
