Prime Minister Tony Abbott is standing by Assistant Health Minister Fiona Nash, insisting she has not breached the ministerial standards conduct over the conduct of a senior staffer.
Mr Abbott also defended his government's ethical standards, telling the opposition it was desperate to find moral fault with coalition MPs, a week after former Labor MP Craig Thomson was convicted on fraud charges.
Senator Nash's chief of staff Alastair Furnival resigned after he failed to divest a shareholding in his wife's public relations company - a requirement of his appointment by the prime minister's office.
The company had links to the junk food industry.
Earlier Mr Furnival had ordered the removal of a health department healthy food-rating website leading to claims he had a conflict of interest in the decision.
Senator Nash later told parliament the department had put up the website prematurely.
Labor has called for her to make a full ministerial statement on what her knowledge of the conflict of interest and her conversations about it with the prime minister's office.
The Greens have called Senator Nash's resignation, accusing her of breaching the ministerial code of conduct and misleading parliament in her initial defence of Mr Furnival.
"Let me make this absolutely crystal clear: the minister has done the right thing," Mr Abbott told parliament on Monday.
"The matter is at an end."
Mr Abbott's office was responsible for vetting the appointment of all ministerial staff.
Labor's health spokeswoman Catherine King asked the prime minister if he was aware of Mr Furnival's conflict of interest when he was appointed the minister's chief of staff.
Mr Abbott said the staffer had been required to divest himself of shares in his wife's company but was "dilatory" in doing so.
"When that became apparent, he resigned," he said.
Mr Abbott said he would back the ethical standards of his government to the hilt against the ethical standards Labor showed in government.
He vowed his government would always act with decency and integrity.
A Senate estimates hearing was told the prime minister approved all appointments of personal staff to ministers, based on advice from the staffing committee.
Liberal frontbencher Eric Abetz said Mr Abbott's chief of staff, Peta Credlin, was a member of the committee and her husband Brian Loughnane, the Liberal party's federal director, also occasionally attended meetings to provide advice as a former ministerial staffer.
Senator Abetz said he understood Mr Furnival's previous role as a lobbyist was disclosed at one of these meetings.