Attorney-General George Brandis has laid the boot into former Greens senators Scott Ludlam and Larissa Waters for walking the parliamentary plank over their dual citizenships.
Senator Brandis, responding to questions from the Greens, said the pair could have dobbed themselves in to the High Court and waited to see if they were still eligible before jumping ship.
"They didn't have to resign, but they did," he said during Senate question time on Tuesday.
"Perhaps that was a catastrophic error of judgement on their part."
Greens leader Richard Di Natale said his colleagues had done "the honourable thing, the decent thing, the right thing" and acted with integrity in standing down.
Senator Di Natale said Nationals senator Matt Canavan had adopted a "half-way house" position in quitting the ministry but remaining in parliament over citizenship concerns, while Barnaby Joyce had stooped even lower.
He pushed the attorney-general to commit to auditing the citizenship statuses of all federal MPs.
Senator Brandis, who steered well clear of calls for a citizenship audit, said he did not deny the two former Greens acted with integrity.
"I suspect they probably acted a little prematurely in resigning," he said.
