Scott Morrison says he will ensure standards are followed, after seeking advice on whether former attorney-general Christian Porter breached ministerial guidelines.
Mr Porter revealed earlier this week he accepted a blind trust to help cover his legal fees for a defamation case against the ABC.
The prime minister told reporters on Thursday he would deal with the matter properly.
"As always, I will carefully ensure that the ministerial guidelines are adhered to," Mr Morrison said.
"I take the matter seriously and we are looking carefully at the arrangements and what the minister will be required to do in order to ensure he was acting consistent with the ministerial guidelines."
Mr Porter said earlier this week he accepted money from a blind trust called the Legal Services Trust to help fund his legal case.
The former attorney-general sued the ABC in March over a story that revealed a now-deceased woman's historical rape allegation against a cabinet minister.
Now serving as the industry minister, Mr Porter has denied the allegation, with the defamation case being settled before trial.
Opposition Leader Anthony Albanese said it was untenable for a minister to accept a blind trust.
"You can't just take money as a cabinet minister from persons unknown and not declare it," he said.
"Why the prime minister needs to have an inquiry on this is beyond me. It's the prime minister who established prime ministerial guidelines, they're his guidelines. There is such a stench around this."
The decision of Mr Porter to accept the blind trust has drawn criticism from former prime minister Malcolm Turnbull, who said politicians should not receive money from undisclosed sources.
A spokesman for Mr Porter told AAP the minister's disclosure was in accordance with the requirements of the register and consistent with previous members' disclosures.
Australian Associated Press