Allowing Deputy Prime Minister Barnaby Joyce to remain in parliament would reward carelessness, his political rival believes, urging the High Court to find him ineligible.
Former independent MP Tony Windsor has joined the case against Mr Joyce, who is one of seven federal politicians embroiled in a dual citizenship saga.
Australians with dual citizenships are banned from entering federal parliament under section 44 of the constitution.
Mr Joyce renounced New Zealand citizenship in August after discovering he had inherited the status from his father.
The government has argued there is a clear distinction between politicians who had known they were a citizen of a foreign power and those who did not, saying Mr Joyce falls into the latter category.
But lawyers for Mr Windsor, including former solicitor-general Justin Gleeson, argued in submissions lodged with the High Court on Tuesday that ignorance was no excuse.
"Acceptance of the argument would reward the careless, and perpetuate the kind of destabilising situations giving rise to the current seven references," his lawyers said.
"A prospective candidate may see it in their interest not to seek advice or ask questions."
Mr Windsor's lawyers argued a lack of knowledge, or lack of a voluntary act in securing or maintaining foreign citizenship, were of no consequence.
"It is the fact of that status at the relevant time that matters, not a person's knowledge (in whatever degree) of the status, nor a person's voluntary act of taking up or retaining that status."
They also argued there was no relevant distinction between citizenship by descent and citizenship acquired by birth.
Mr Windsor lost the seat of New England to Mr Joyce in 2016 after a bitter and tight election battle.
He is the only third party granted leave to take part in the proceeding against a politician, other than the politician themselves and the attorney-general.
Mr Joyce's case, along with those of six other federal politicians, will be heard in the High Court in Canberra between October 10 and 12.
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