Shadow treasurer Chris Bowen said predicting the Senate outcome was “a mugs game” and has begun threatening the crossbench to prepare if Labor wins in May.
“We start with a moral authority and a mandate from the Australian people,” he said.
Election analyst Kevin Bonham said One Nation was almost certain to regain the seat it lost through the defection of Fraser Anning in Queensland, with former senator Malcolm Roberts likely to return. They will also challenge for a spot in NSW.
The Greens are “no sure thing” in Queensland or South Australia, he said, with prominent senators Sarah Hanson-Young and Larissa Waters falling short of the 14.3 per cent quota required and facing a battle to hold onto their positions against Labor and conservative opponents.
Greens leader Richard Di Natale said the Senate is “going to be critical at this election”.
“It’s the Greens in the Senate that will hold a future Shorten Labor Government to account,” he said.
Legislation needs a majority of 39 votes to pass the Senate. Labor and the Greens currently have 35 seats combined.
“Based on national polling the likely prospect is about two gains and they fall just short of a combined majority,” Mr Bonham said.
“The first cab off the rank will be Centre Alliance. There is a realistic prospect that you have Labor-Greens-Centre Alliance combined majority.
“If they win in the House of Representatives comfortably then they should get a manageable Senate without having to rely on votes from One Nation and Cory Bernardi,” he said.
Tally room election analyst Ben Raue, who also works for Get Up!, agreed this was the most likely scenario, with the Greens and Labor facing an uphill battle to get more than half of the Senate seats available in each state to win a majority.
The two Centre Alliance senators Rex Patrick and Stirling Griff are on six year terms. They will hold their seats until 2022.
Senator Patrick said the partywould kick off its campaign in Adelaide on Friday on a platform of protecting the Murray-Darling, local manufacturing and electric vehicles. He said the party was confident of picking up an extra seat.
Former NXT Senator Skye Kakoschke-Moore will be their number one candidate, while former leader Nick Xenophon will take no part in the campaign.
“He got out of politics and intends to stay out,” Senator Patrick said.
He said the party would target Labor over its changes to franking credits.
“It is not proper to make changes once people have retired and set themselves up in a particular position,” he said.
Grandfathering franking credit refundability was one option, “but it would destroy the revenue base,” he said.
Senator Patrick said he was open to limiting the number or value of properties that could be negatively geared but would not support Labor’s position to abolish it for all future purchases of existing properties.
He outright rejected Labor’s pledge to lift the top tax rate for workers earning $180,000 a year from 47 to 49 per cent.
A failure to get the measure through the Senate would mean a further $1 billion hit to Labor’s revenue measures.
Eryk Bagshaw is an economics correspondent for The Sydney Morning Herald and The Age.