Australia's Greens have launched their election bid to win the balance of power in the upper house.
Opinion polls show the Greens on track to win at least two extra Senate seats in the 21 August election, which could give the party the deciding vote over contentious legislation.
That could force a returned Labor government to harden its tax plans for big miners.
And it could undermine for the Liberal coalition plans on climate policy and to re-establish an offshore refugee processing centre on the Pacific island nation of Nauru.
A Nielsen poll on Saturday found Prime Minister Julia Gillard heading for defeat, with government support at 48% compared to 52% for Tony Abbott's opposition.
The Greens, with about 12% of the national vote, are running candidates in all 150 lower house seats.
But the party's campaign is focused on extra seats in Senate, where the Greens currently share the balance of power with two independents.
Greens leader Bob Brown says he wants the government to firm up its planned 30% tax on big iron ore and coal mines, and big mining companies to pay more for crucial infrastructure projects.