The major parties have moved closer together on "cruelty" and that will be reflected in their preference deals, Greens leader Christine Milne says.
The coalition is reportedly considering an agreement with the ALP that would put the Greens last in the minor party's most winnable lower house seats, Melbourne and Grayndler.
The move would mean Greens deputy leader Adam Bandt facing an uphill battle to hang onto his party's only House of Representatives seat.
The Greens are also given a chance in Anthony Albanese's Sydney seat of Grayndler, which the deputy prime minister holds by 4.2 per cent.
Senator Milne said the major parties were moving closer together on policy.
"They are close together on cruelty to refugees and their horrible solution of warehousing people on Manus Island and at Nauru," she told reporters in Hobart.
"They're very close together in terms of destroying the Tarkine (wilderness in Tasmania).
"They are close together in terms of refusing to lift Newstart, they're refusing to support single parents.
"They have moved together on all those things so it wouldn't be surprising if they preferenced each other ahead of a progressive alternative."
Senator Milne said voters should make their own decisions about who to give their preferences to on polling day.
"If you want to have an Australia that is respected internationally, which is a caring society and which looks after the environment, then the Greens are the obvious choice," she said.
The Greens are meanwhile urging independent Senator Nick Xenophon to do a preference swap in South Australia to head off a coalition bid to take control of the Senate.
SA Greens Senator Sarah Hanson-Young is fighting to retain her seat with the final SA spot likely to go to her or the third candidate on the Liberal ticket.
Former Greens leader and party heavyweight Bob Brown was in Adelaide on Thursday urging Senator Xenophon to do a preference deal to ensure both the "progressive" senators were returned.
"I'm calling on Nick Xenophon to make it clear that he will be giving preferences to Sarah ahead of the coalition," Dr Brown said.
