Mining tax the only budget plan: Grylls

The Nationals' proposed mining tax is the only plan on offer to save WA's beleaguered budget, leader Brendon Grylls says.

The WA Nationals say their proposed mining tax shows they are the only party with a plan to stabilise the state's struggling budget.

Leader Brendon Grylls says the mining industry's untruhful campaign against his $5 a tonne tax would grow during the state election, and West Australians need to show they are not servants of multinational miners and "faceless" board members.

Mr Grylls predicts the Liberals' plan involves "crossing its fingers" and will cave and agree to the tax, which he says will reap $7.2 billion over four years.