Culture Secretary Tessa Jowell has denied any conflict of interest arising from her husband's financial dealings.
It has been claimed there is a link between a loan application she signed on the couple's house, and money which Italian prosecutors allege was a bribe.
Ms Jowell, who has been given No 10's backing, said: "I am absolutely happy everything has been done properly."
Shadow Commons leader Theresa May wants a ruling on whether Ms Jowell breached the ministerial code of conduct.
Cabinet secretary Sir Gus O'Donnell is expected to respond to Mrs May's call within the next few days.
'Swirling around'
Asked if she thought there should be an inquiry, Ms Jowell said someone needed to tell her first what she had done wrong.
Her husband, international lawyer David Mills, denies taking a £344,000 bribe from Italy's Prime Minister Silvio Berlusconi.
But Labour MP Tony Wright - chairman of the Commons public administration committee - told BBC Radio 4's Today programme: "I think (Ms Jowell) is in some difficulty in the sense that all this stuff is swirling around and there's nothing much she can do about it, except say it is completely unfounded.
"Has the ministerial code been adhered to, particularly obviously in relation to any requirement to notify in relation to financial transactions?"
"It all seems profoundly unsatisfactory. I'm sure that at some point in the past she wishes that over the breakfast marmalade she had said to her husband 'Could you not do a bit of gentle conveyancing in the Home Counties?'
"We are in murky Italian corruption territory. I think nobody knows what's going on really. We shan't know for a long time. We probably shan't know, in some sense, ever."
However, Mrs May said it was not essential to know about the Italian investigation into Mr Mills.
"All I'm asking is, has the ministerial code been adhered to, particularly obviously in relation to any requirement to notify in relation to financial transactions."
The Sunday Times alleges it has identified a link between a loan secured on a house jointly owned by the couple and money which Italian prosecutors allege was a bribe.
'Not improper'
Ms Jowell co-signed a mortgage on the £700,000 home in Kentish Town, north London, which she owns with Mr Mills, but said the deal did not mean a conflict of interest.
"I agreed that we would take out a loan on our house. That is not unusual, it's not improper, and it's certainly not illegal," she said.
On Monday the prime minister's official spokesman said Ms Jowell had Tony Blair's full support.
"I told no lies, but I turned some very tricky corners, to put it mildly"
Italian officials say Mr Mills, 61, was paid to give false evidence in court for Mr Berlusconi.
Mr Mills admits writing a letter to his accountants where he appears to be describing a payment, but claims he was inventing a scenario to get tax advice.
In a statement, Ms Jowell said: "I signed a charge over our jointly owned home to support a loan made to my husband alone by his bank.
"I am satisfied that no conflict of interest arose out of this transaction in relation to my ministerial duties.
"As is standard practice in relation to legal proceedings, it would be inappropriate for me to comment further."
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