David Cameron has given his support to Maria Miller after the Parliamentary Commissioner for Standards opened an inquiry into her expenses.
The prime minister said his culture secretary had "excellent answers" to questions about her expenses claims.
Labour MP John Mann submitted a complaint about her claims on Tuesday.
It follows reports she had allowed her parents to live in a property on which she claimed £90,718 in second home allowances during the last parliament.
Mrs Miller has said her expenses were "absolutely in order" and "in complete accordance with the rules".
Mr Cameron, speaking as he arrived in Brussels for a European summit, said Mrs Miller was doing "an excellent job".
The Daily Telegraph reported that Mrs Miller had been claiming expenses for her second home in south London, while her parents were living there, with her "main home" located in her Basingstoke constituency.
Her parents, John and June Lewis, have apparently been living at the property since selling their home in Wales in 1996.
Following the report, Mr Mann wrote to the Parliamentary Commissioner for Standards, John Lyon, saying the arrangement was "identical" to that which meant former Labour minister Tony McNulty was required to pay back more than £13,000 in expenses in 2009.
The commissioner ruled that Mr McNulty had effectively "subsidised" his parent's living costs from the public purse.
A spokesman for Mrs Miller said her "expenses have been audited twice and found to be wholly proper and above board".
"Any suggestion to the contrary is simply untrue," he said, adding that the minister would "fully co-operate" with the inquiry.
But, during exchanges on future business in the Commons, Labour's Angela Eagle raised a follow-up report in the Daily Telegraph, which said an aide to Mrs Miller had called the journalist working on the expenses story to "flag up" the culture secretary's involvement in on-going negotiations on the future of press regulation.
The Daily Telegraph has also reported that Downing Street communications chief Craig Oliver mentioned press regulation in a telephone call to the newspaper's editor about the expenses story.
Ms Eagle, the shadow Commons leader, said: "The government seems to want to threaten the press with statutory underpinning to control the news agenda."
No 10 denied doing anything wrong: "The secretary of state [Mrs Miller] had some concerns about the way that investigation was conducted. She set those out in a letter to the editor. Craig Oliver was simply reflecting those concerns."
A Department for Culture, Media and Sport spokeswoman said: "Mrs Miller's special adviser raised concerns with a journalist about the nature of an approach to Mrs Miller's elderly father.
"Her adviser noted that Mrs Miller was in contact with the paper's editor and would raise her concerns directly with him, which Mrs Miller did subsequently."
The spokeswoman said there was no link between this intervention and discussions over the future of press regulation.