The world’s biggest mining companies producing iron ore from Australia aren’t paying their fair share in taxes, according to a lawmaker who wants a 20-fold raise in a state levy that’s been unchanged since the 1960s and the era of imperial pounds, shillings and pence. The proposal has “overwhelming” support and Rio Tinto Group and BHP Billiton Ltd.’s objections don’t stack up, according to Brendon Grylls, Western Australia’s Nationals party leader.