Labour is set to refer Jeremy Hunt to the parliamentary commissioner for standards over an apparent delay in declaring his property interests.
The health secretary has apologised after it was discovered he made errors over the purchase of luxury flats.
Mr Hunt has a 50% interest in a firm – set up with his wife in October – but he did not declare it to Companies House until six months later.
His spokesman said it was an “honest administrative mistake”.
The Telegraph said Mr Hunt set up Mare Pond Properties in 2017 to buy seven flats in the Ocean Village development in Southampton.
His spokesman said: “Jeremy’s accountant made an error in the Companies House filing, which was a genuine oversight.”
The minister did inform the Cabinet Office of his involvement with the company after it was set up, he added.
The department has since said there was no breach of ministerial code.
By BBC political reporter Jessica Parker
It won’t surprise anyone to know that legislation in this area is a little complicated.
But essentially, in 2016, the 2006 Companies Act was amended.
Companies must now register their persons of “significant control” – so-called PSCs – with Companies House.
Initially the requirement was to update this information on an annual basis but then the law was further changed to within 28 days.
What counts as a PSC? Well the conditions include someone who owns more than 25% of the shares in a company.
And it’s true to say that, technically, failure to stick to these rules could result in a fine or even up to two years in prison.
But in reality, it seems very unlikely that Jeremy Hunt is going to face any serious legal consequences.
Companies House have said their “primary aim is to seek compliance”, suggesting that they are taking a relatively gentle approach in dealing with such oversights which, I’m told, are not uncommon.
Jon Trickett, Labour’s shadow secretary for the Cabinet Office, said Mr Hunt’s behaviour was “simply unacceptable” and his party would be taking the matter further.
“Labour will today refer Jeremy Hunt to the standards commissioner to look into this serious breach,” he said.
“He should have had the decency to refer himself rather than sweep this under the carpet.”
Mr Hunt’s spokesman said: “Although there was no personal gain involved, Jeremy accepts these mistakes are his responsibility and has apologised to the parliamentary authorities.”
A Downing Street spokesman said it was right that the minister had apologised for the “administrative oversight”, but agreed with the Cabinet Office that there was no breach of the ministerial code.
“We consider the matter closed,” he added.