WA Greens Senator Scott Ludlam has had his submission to the hearing that could see him lose his seat dismissed by a High Court justice.
The six Western Australian senators elected in November could face another ballot if the High Court — sitting as the Court of Disputed Returns — declares the result invalid at the completion of a trial due to start next week.
The result in WA has already been the subject of an investigation by former Australian Federal Police chief Mick Keelty after 1,370 ballots went missing during a recount.
In November, the Australian Electoral Commission (AEC) filed a petition calling for the WA Senate election to be declared void.
The Palmer United Party and the Labor party have launched separate actions seeking that the first vote be declared the official result.
Senator Ludlam, who was elected to the sixth position after the recount, filed a petition in December saying that if the court was satisfied that he was not elected, the election of all six senators should be declared void.
However, his petition will not be included in next week's trial, after Justice Kenneth Hayne on Tuesday dismissed it.
He also ordered Senator Ludlam pay costs for six of the other seven respondents.
The AEC did not seek costs.
In the initial count, the final two WA Senate places went to Zhenya Wang of the Palmer United Party (PUP) and Labor's Louise Pratt.
But in the recount, without the missing votes, Wayne Dropulich of the Australian Sports Party and Senator Ludlam were elected.