If Home Affairs Minister Peter Dutton is referred to the High Court, Prime Minister Scott Morrison warns other MPs will follow him.
Questions still remain over whether Mr Dutton is eligible to sit in parliament given his financial interests in childcare centres, which get federal funding to pass through to parents.
Former Liberal MP Julia Banks is prepared to vote to refer Mr Dutton to the High Court to test whether he meets Section 44 of the constitution, which bans people from parliament if they get money from the Commonwealth.
“There are three other house members that have the same issues that have been suggested about Peter Dutton,” Mr Morrison told reporters in Buenos Aires on Saturday local time.
“So any principled position, any consistent position, anyone seeking to be truly fair about this would apply the same rule to all of those members.”
They include independent Kerryn Phelps, who gets federal funding to pass onto patients in her role as a GP.
“The government isn’t seeking to refer any of those members, but if the parliament sought to do so then it would only be the principled thing to do to apply the same treatment to all the members affected,” Mr Morrison said.
The minority coalition government now holds just 74 of 150 lower house seats, and Labor could successfully refer Mr Dutton if it secures votes from six out of the seven crossbenchers.
Defence Minister Christopher Pyne this week dismissed concerns about a potential referral, but threatened a tit-for-tat attack on other MPs if it went ahead.
At the height of the Liberal leadership crisis, Solicitor General Stephen Donaghue provided advice saying he could not categorically determine Mr Dutton’s status and only the High Court could decide.
Mr Dutton has dismissed questions over his eligibility, while Dr Phelps also has legal advice she says puts her in the clear.