WA Nationals leader Brendon Grylls is keeping up his fight for a $5 tax per tonne of iron ore.

Mr Grylls say he will not back down on the plan to hit big mining companies, which is a central part of the party’s mission to gather public support.

The state’s Liberal party still rejects the idea, with Mines and Petroleum Minister Sean L'Estrange say the Government had no intention to change standing agreements.

Mr Grylls was returned to the National Party leadership in August while pledging a 20-fold increase on the iron ore production levy paid by BHP and Rio.

“I'm not in the position of negotiating, the Nationals have a very clear policy ... the negotiation is really with the Liberal Party around are they prepared to accept a new revenue source?” he told reporters.

“Those discussions are progressing well, advancing weekly.”

Mr Grylls says polling shows more people are supportive of the royalty increase than opposed.

The mining lobby will wage war against the plans.

“There is no doubt we are going to have to go out to the public of Western Australia and explain these companies are taxed fairly and squarely,” Chamber of Minerals and Energy chief executive Reg Howard-Smith said.

“We are quite confident that when you explain to people... this will make us the most taxed regime in the world, in a very competitive market, that I think there will be a change in attitude towards the tax.”