A constitutional expert says it would be wise for ministers under a High Court cloud to step aside or the federal government could face legal action over its decisions.
Five members of parliament, including Deputy Prime Minister Barnaby Joyce, face a High Court test of their eligibility under section 44 of the constitution, which bans dual nationals from being MPs.
Another two, including cabinet minister Fiona Nash, will be referred to the court by parliament next week.
One ministerial colleague, Matt Canavan, stood aside when issues were identified about his status.
Professor George Williams, one of the nation's foremost constitutional experts, says it's difficult to see that any of the seven MPs facing the court had taken reasonable steps to renounce their citizenship of other countries.
He said that while no law was likely to be undone because it was "tainted" by the election of an ineligible member - based on previous High Court decisions - there were question marks over government decisions.
"The situation of ministers is less clear," Prof Williams told the National Press Club in Canberra on Wednesday.
"The wisest course is for them to refrain from making decisions or to step down pending the outcome of the High Court hearing."
He said this was because their authority to run their departments and to make decisions under legislation depends upon the law regarding them as being properly appointed.
Section 64 of the constitution says that "no minister of state shall hold office for a longer period than three months unless he is or becomes a senator or a member of the House of Representatives".
"If current ministers are ruled in breach of section 44, they will have made many decisions without apparent legal support from when the three-month period of grace ran out late last year," Prof Williams said.
He said decisions about contentious matters such as Adani's Carmichael coal mine in Queensland might be challenged in the courts.
The University of NSW academic said the issue may get much worse, and after the court makes its decisions there may be merit in an audit of all MPs which he believed could uncover 20 or more members with eligibility problems of various kinds.
However, an audit would face the difficulty of some members refusing to comply and others arguing it's a matter for the courts.
Asked whether Prime Minister Malcolm Turnbull was right to say he was very confident the court would clear his ministers, Prof Williams said such comments were unwise.
The court will hear the cases from October 10 to 12.