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 the 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.
But 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.