The Liberal Party has announced it will be preferencing the Greens last in all 150 House of Representatives seats.
Coalition Leader Tony Abbott says it reflects the Liberals' opposition to what he calls the Greens' fringe economic policies and its belief in open borders.
Tony Abbott's move is designed to eliminate the Greens from the House of Representatives.
It means the Greens' Deputy Leader Adam Bandt now faces a tough challenge to retain his seat of Melbourne - the only lower house seat won by the Greens in the 2010 election.
Mr Abbott says he doesn't regret helping Mr Bandt to be elected in 2010 by preferencing the Greens before Labor then, but times have changed.
He says the Greens have had too much influence over the outgoing Labor minority government.
"This election is about producing a strong government, a majority government with a clear majority in the parliament. It's about having strong economic policies which protect your job security, which improves your cost of living. That's what it's all about. But it's the last thing we'll get from a parliament which is over-influenced by people like the Greens."
Under the preferential system of voting for the House of Representatives, voters are required to number the candidates on the ballot paper in order of preference.
To win, a candidate needs to secure an absolute majority.
If that doesn't happen after primary, or first preference, votes are counted, then the candidate with the least number of primary votes is eliminated and those votes re-allocated in accordance with voters' second preferences.
Parties go to great effort to advise voters on how they would like preferences to be distributed in a way that would benefit them most.
Adam Bandt won Melbourne for the Greens ahead of the Labor Party candidate in 2010, with the help of re-allocated preferences from the Liberal Party candidate, who was placed third after the counting of primary votes.
Mr Abbott, who has ruled out forming a minority government with any independents or minor parties, has not ruled out doing preference deals with candidates or parties, other than the Greens.
"There is a world of difference between the Greens and as far as I am aware, just about everyone else who is contesting this election campaign. Because everyone else in this campaign supports economic growth and supports a more prosperous economy. The Greens on the other hand, they want a bank levy, they want a wealth tax. These are quite frankly, fringe economic policies, to put it at its kindest."
Adam Bandt says he's still hopeful of being able to hold onto his House of Representatives seat, without the help of preferences from the Liberals.
"From day one we have said the Greens will hold the seat of Melbourne in our own right. That's our goal and not to have to rely on preferences from any other party. And we have worked steadily towards that over the last few years. We've also been a strong voice in the parliament at a time when Labor and Tony Abbott are engaged in a race to the bottom."
Prime Minister Kevin Rudd is claiming to not know how the Labor Party will urge its supporters to allocate preferences on September 7.
But he is promising the party would not enter into any agreements to form minority government if the election returns a hung parliament.
"All preference matters are handled by the National Secretary of our party and I'm not aware of what agreements have been reached and frankly I intends to leave it all to them. These are organisational matters. Let me also be very plain about this. That we'll will not be entering into any coalition agreements. We won't be having any negotiated agreements. We won't have any deals with any independents or any minor party.Our objective is to be a majority government in our own right."
As well as putting Adam Bandt in trouble, the Liberal Party's preferences decision also probably rules out any chance the Greens had of winning other inner-city seats such as Batman in Victoria and Grayndler and Sydney in New South Wales.
The Liberals say their preferences decision so far relates only to the House of Representatives, and they have not yet decided who they will preference in the Senate.
If the party decides to preference against the Greens in the Upper House as well, then the South Australian Senate seat of the Greens' Sarah-Hanson Young and the West Australian Senate seat of the Greens' Scott Ludlum could hang in the balance.
