Justice Minister Michael Keenan has hinted authorities could investigate former Greens senator Scott Ludlam over his citizenship oversight.
Mr Ludlam resigned last week after revealing he is a dual Australian/New Zealand citizen and Mr Keenan says it was a "remarkable oversight".
Mr Ludlam insists he was unaware he was still a New Zealand citizen until last week.
Mr Keenan says the rules about dual nationality are clear and well known to every member of Australian parliament.
"It's been well and truly tested," he said.
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"We've had by-elections based on this when people have been elected."
Whether Mr Ludlam could face further penalties for his oversight is a matter for other authorities, Mr Keenan says, but he does expect the matter to be investigated.
"I'm sure that they will and they will have to make judgments about how to proceed but that's really not up to me," he said.
