Cabinet Minister Baroness Warsi is facing fresh allegations of breaching House of Lords rules, a week after she referred herself to a parliamentary watchdog over her expenses claims.
The Sunday Telegraph claims the Conservative co-chairman may have breached the Lords code of conduct by failing to register business interests.
The newspaper alleges she failed to declare a controlling stake in a spice manufacturing firm, called Rupert's Recipes, with the Lords authorities.
But the peer has denied the claims and insisted she had stuck by the rules for declaring shareholdings and directorships.
The newspaper said February accounts for Rupert's Recipes showed Baroness Warsi held 60% of its shares - sufficient to require a public declaration.
It said she was also listed as a director of the firm from February 2009 until July 6 2010, two months after she entered the Cabinet.
Sources suggested the shares were transferred into her name for a short period only and were then passed into the hands of her husband.
They also said there was no requirement to register unpaid directorships before a strengthening of the upper house rules last year.
In a statement, Baroness Warsi said: "My shareholdings and, before becoming a minister, directorships have at all material times been disclosed as required on the Register of Lords' Interests and to the Cabinet Office and on the register of ministerial interests."
Labour also raised questions about the presence of business associate Abid Hussain on an official trip to Pakistan by the senior Tory.
Shadow cabinet office minister Michael Dugher compared the case with that of Liam Fox - who quit as Defence Secretary after his relations with a lobbyist breached the ministerial code.
"This looks like the Liam Fox/Adam Werritty case all over again - with ministers allegedly being accompanied on official trips by their private business associates," he said.
"Baroness Warsi has urgent questions to answer: were House of Lords rules broken in this case?
"What was Mr Hussain doing on an official Government trip in the first place? Was he security vetted and was his presence cleared by the Cabinet Secretary or by Number 10?
"After his reluctance to take action against Jeremy Hunt, David Cameron now needs to show he is prepared to make sure his ministers show the highest standards of behaviour."
Baroness Warsi said: "Neither I nor the Conservative Party nor the Government has ever met the costs of foreign visits by Abid Hussain."
Earlier in the week, she asked Lords Commissioner for Standards Paul Kernaghan to look
into the claims about her expenses. She denies any wrongdoing.