One Nation senator Rod Culleton has had a change of heart, declaring he will now attend a directions hearing about the validity of his election, despite earlier ruling out turning up.

The Senate has asked the High Court to investigate the eligibility of Senator Culleton, and former Family First senator Bob Day, with the directions hearing set for next Monday.

Senator Culleton previously said he would not attend because the Senate is sitting next week, but has told 7.30 he has changed his mind.

"That's just changed in the last 10 minutes before coming to the studio," Senator Culleton said.

"I just got the submissions from the government solicitors and at one stage I thought I'd be just wrestling with smoke down there, but it's important that I go down to make sure that all the dates line up because they're trying to express run it prior to Christmas."

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Senator Culleton said he still planned to represent himself in court and thought it was a "positive move" to attend in person.

"Now that I've finally got the submissions, only a couple of days before the hearing date, I think it's a positive move to go down there on Monday."

The Federal Government wants Senator Culleton's election investigated because he had been convicted of an offence carrying a jail term of one year or more at the time of the July 2 poll.

That may make him ineligible to sit in the Upper House, even though the conviction has since been quashed.

The challenge against Mr Day relates to a possible financial interest he had in his Adelaide electoral office and whether it breached the pecuniary interest rules for parliamentarians.