Veteran Liberal senator Eric Abetz is being urged to provide proof he renounced his German citizenship before being elected to the Australian parliament.
Greens senator Peter Whish-Wilson pointed the finger at Senator Abetz in parliament on Wednesday, as he paid tribute to two former colleagues, Scott Ludlam and Larissa Waters, who resigned in July after discovering they were dual citizens.
He called on Senator Abetz to come to the chamber and provide documentation showing exactly when he renounced his German citizenship.
Liberal colleague Ian Macdonald asked the comment be withdrawn given Senator Abetz is absent from parliament this week because of a family illness.
Senate President Stephen Parry has been asked to decide whether the comment should be withdrawn.
Senator Abetz has previously described the claims as "absurd", insisting they have been comprehensively disproved.
He says he became an Australian citizen in 1974 and argues it was not possible under either Australian law or German law for him to have been a dual-citizen.
It follows the referral on Tuesday of three senators to the High Court, sitting as the Court of Disputed Returns, to determine their eligibility.
The Senate referred stood-down cabinet minister Matt Canavan, as well as Mr Ludlam and Ms Waters, amid revelations he is an Italian citizen and therefore, ineligible to sit as an Australian parliamentarian under the constitution.
A fourth senator, One Nation's Malcolm Roberts, will be referred to the court on Wednesday afternoon, amid questions over whether he was a dual-citizen at the 2016 federal election.