West Australians could find out as early as tomorrow night if they will be ordered back to the polls for a fresh Senate election.
A two-day hearing over the bungled election begins in Melbourne today before High Court Justice Kenneth Hayne. The court will sit as the Court of Disputed Returns.
The Australian Electoral Commission petitioned the court to hold a re-run poll after 1370 ballot papers disappeared during a re-count and left the result under a cloud.
The Palmer United Party's Dio Wang and Labor's Louise Pratt originally won the final two Senate seats but the re-count gave them to the Australian Sports Party's Wayne Dropulich and the Greens' Scott Ludlam.
Lawyers for the Liberal Party, Labor and PUP are challenging the need for a new poll, arguing the AEC should use the original counts conducted at the polling booths from which the missing ballot papers came.
Labor and PUP also want the court to review about 945 ballot papers they claim were incorrectly counted during the re-count.
They argue that if these votes were included, the loss of the 1370 votes would be immaterial.
Justice Hayne's ruling will be final with no avenue of appeal to the Full Bench of the court.
Political sources said it was possible Justice Hayne could hand down his ruling tomorrow night so the process for a new election could begin, though it is more likely he will wait a day or two at least.
The AEC asked the court to rule by March 18 at the latest so the election writs could be issued three days later for a minimum 33-day campaign.
The latest that an election could be held - enabling the senators to take their places in the new Senate from July 1 - is April 26.
A fresh poll would cost taxpayers $13 million and could complicate Tony Abbott's ability to get legislation through Parliament. The Government will have to rely on Right-leaning independent senators but Liberals fear their third candidate, Linda Reynolds, might not win her seat because support for the party has waned. That would make the Prime Minister's task of negotiating with the Senate harder.
If Justice Hayne accepts the argument of Labor and the PUP, the case could drag out for weeks as ballot papers are re-examined.