Cabinet minister Mathias Cormann has reignited the dual-citizenship debate, insisting a Labor MP is sitting in breach of the constitution.
Senator Cormann pre-empted Wednesday's High Court ruling on the eligibility of Labor senator Katy Gallagher to sit in parliament for holding British citizenship when elected.
"Clearly right now there are people in the House of Representatives in Bill Shorten's team who are there in breach of the constitution," Senator Cormann told reporters in Canberra on Monday.
He singled out the case of Queensland MP Susan Lamb, who obtained British citizenship by descent but has been unable to provide adequate evidence in order for it to be renounced.
"Susan Lamb by her own admission is a British citizen," Senator Cormann said.
"Our constitution essentially makes it very clear that to be eligible you've got to be an Australian citizen only - which Susan Lamb clearly is not," he said.
But Ms Lamb claims she was validly elected to parliament as she took "all reasonable steps" to renounce her British citizenship.
In an emotional speech to parliament in February she explained how her estrangement from her mother prevented her from obtaining her parent's marriage certificate.
The High Court's decision on Senator Gallagher's citizenship status is expected to have flow-on effects for others in the federal opposition.
The eligibility of MPs Justine Keay and Josh Wilson is also under government scrutiny.
