The Australian Electoral Commission says a fresh WA Senate election is needed because the 1370 people whose ballot papers were lost during the bungled recount were effectively "prevented from voting".
In a submission to the High Court, sitting as the Court of Disputed Returns, the AEC also argues there is nothing that can be done to overcome the impact of the loss of the ballot papers.
The case resumes today with a directions hearing before Justice Kenneth Hayne in Melbourne.
It is understood the Palmer United Party will use the hearing to try to have the Greens' petition, which also endorses the need for a fresh poll, struck out.
A fresh Senate-only election in WA would cost taxpayers $13 million and could make it harder for Prime Minister Tony Abbott to get legislation through Parliament. The Liberals, Labor and PUP are trying to persuade the court to reinstate the results of the original count, in which the Liberals won three seats, Labor two and PUP one.
One argument the Liberals are keen to pursue is that the election of the first four senators - their three and Labor's Joe Bullock - is not under any cloud.
A re-count was ordered because the result hinged on just 14 votes at a crucial point of the count. The re-count favoured the Greens and the Australian Sports Party by 12 votes, and they each won a seat at the expense of Labor and PUP, but along the way 1370 ballot papers were lost, plunging the result into doubt.
As part of their case, Labor and PUP have also claimed election officials incorrectly counted hundreds of ballot papers that cost their candidates their seats.
Of 949 disputed votes, Labor believes at least 177 should be changed in its favour, while PUP has identified 74.
But the AEC said in its submission that because the number of missing votes "significantly exceeds" the number of disputed ballot papers, it was unnecessary to re-examine them because "no petitioner asserts that there are a sufficient number of other errors that would overcome the effect of 1370 disenfranchised voters".
The AEC said the 1370 people whose votes vanished were entitled to have their vote included when the re-count was held.
Given Australia had a system of compulsory voting and secret ballots, the votes of all people must be scrutinised and "close enough" was not acceptable.