Home Affairs Minister Peter Dutton is refusing to check his eligibility to sit in Parliament, insisting the legal advice is on his side.
But former prime minister Malcolm Turnbull and Labor say the High Court needs to check if the minister's family financial interest in childcare centres makes him ineligible to sit.
"I have taken advice in relation to my position, which put the question beyond doubt," Mr Dutton told parliament on Thursday
Mr Turnbull says Mr Dutton's constitutional position needs to be clarified, comparing it to the case of former deputy prime minister Barnaby Joyce.
"The point I have made to @ScottMorrisonMP and other colleagues is that given the uncertainty around Peter Dutton's eligibility, acknowledged by the Solicitor General, he should be referred to the High Court, as Barnaby was, to clarify the matter," he tweeted on Wednesday night.
Section 44 of the constitution disqualifies anyone who has a "direct or indirect pecuniary interest" in any agreement with the Commonwealth.
Mr Dutton's childcare centres directly receive government funding under recent law changes, and the money is passed through to parents.
Mr Dutton, who did not achieve his ambition to replace Mr Turnbull in last month's Liberal leadership stoush, said his former boss should "enjoy his retirement".
"Mr Turnbull never raised once with me any issue around section 44," the minister told 2GB radio.
"His staff never raised it with my office, he never asked me for the legal advice that I had that showed I had no problem at all."
Former Liberal deputy leader Julie Bishop said MPs had a "personal responsibility" to ensure they were eligible to sit in parliament.
"We have seen in recent times steps taken by members of parliament to clarify their status," she told reporters.
Prime Minister Scott Morrison says he won't act on Mr Turnbull's advice.
"I think people have had enough of the lawyer's picnics on these sort of issues," he told reporters.
Barnaby Joyce, who caused major headaches as Mr Turnbull's deputy prime minister when he refused to resign after he got an ex-staffer pregnant, accused his old boss of trying to bring down the government.
"It seems like he has an active campaign to try and remove us as the government. Boy, that is bitterly disappointing," he told reporters.
Solicitor General Stephen Donaghue advised he could not categorically determine Mr Dutton's status, as only the High Court could, but found on balance the minister was "not incapable" of sitting as an MP.