Prime Minister Tony Abbott is being urged to give a full account of when his office was told about a potential conflict of interest involving the chief of staff to Assistant Health Minister Fiona Nash.

Senator Nash has confirmed her chief of staff asked the Health Department to remove a food rating website - which disappeared a day after it went live - on her behalf.

It has emerged the staffer, Alastair Furnival, holds a previously undeclared stake in a lobbying firm which represents food companies, but Senator Nash insists there is no conflict of interest.

"My chief of staff is not involved in the operation of that business," she said.

In response to Opposition questions in Parliament, the Prime Minister on Thursday said he would look into the matter.

"I am concerned to ensure that the ministerial guidelines have been fully complied with," he said.

According to the Government's Statement of Standards, ministerial staff are required to divest themselves of interests in any business involved in the area of their minister's responsibilities.

Opposition frontbencher Tony Burke questioned why the Prime Minister appointed Mr Furnival, a query Mr Abbott initially sought to brush off.

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"This matter has been raised on a number of occasions in the Senate, and I would refer the (member) to the answers that have been given in the Senate," Mr Abbott said.

But the Prime Minister was less strident in response to another question from Mr Burke:

"Is the Prime Minister aware that Minister Nash did not disclose at the meeting of the Australia and New Zealand Food Regulation Ministerial Council, that the Minister chaired in December, that her chief of staff held a shareholding in a food industry lobbying firm, notwithstanding that conflicts to be declared were on the agenda?

"Why hasn't the Prime Minister taken any action in accordance with his own ministerial code of conduct?"

Mr Abbott replied: "I am sure that the member opposite is raising these matters because he is concerned to ensure that the ministerial guidelines have been fully complied with.

"I am concerned to ensure that the ministerial guidelines have been fully complied with as well.

"I will take the question on notice and if there is anything more to say I will say it."

Details given to PM with 'appropriate timing'

In the Senate, at the same time, Labor was continuing to press Senator Nash on the matter.

Labor senator Penny Wong asked: "On what date did the Prime Minister approve the appointment of her chief of staff?

"Was the Prime Minister informed about her chief of staff's shareholding in a food industry lobbying firm before or after his appointment?"

Senator Nash said "all appropriate steps were taken" to ensure there was not a conflict of interest.

"It was all done in a very thorough and diligent manner," she said.

She said "all information around her chief of staff" was given to the Prime Minister's office "in accordance with appropriate timing".

But Senator Wong called that answer "dropping the Prime Minister's office in it".

Senator Nash says Labor is pursuing the matter to avoid debating substantive policy issues.

The controversy has arisen after Mr Furnival phoned a senior Health Department official last week to order the removal of the website promoting a new healthy star food labelling system.

Yesterday, that official emailed stakeholders in the policy to inform them that she had been removed from its direct control.

In response to questions, Senator Nash said she had no direct knowledge of the staffing changes and found out when others did.