Health Secretary Steve Barclay has allegedly been accused of “bullying” and “bad behaviour” by civil servants.
Officials from the Department of Health have “raised” concerns about his conduct to staff working under him, sources told the Guardian.
But a spokesman for Mr Barclay said the allegations were “totally untrue”.
Sources said the civil servants had informally complained to Chris Wormald, the department’s permanent secretary.
One source said there were “a lot of unhappy people at the Department of Health just now” partly because of Mr Barclay’s behaviour.
Others said “everyone finds him quite challenging” and that he “deliberately ignored” staff who tried to talk to him and was “constantly angry”.
Mr Barclay allegedly “blasted” staff in front of other people - with his behaviour now meaning officials “don’t want to have meetings with him”.
Another source said: “Barclay’s style is very macho … He would say that he’s forensic. But in reality he’s a micro-manager. He hauls people over the coals and is generally a bit unpleasant.”
Sources added that officials in his private office had “borne the brunt” of his behaviour.
Rishi Sunak is already facing the fallout of his ex-Deputy PM Dominic Raab resigning on Friday after bullying claims were upheld against him.
Questions have been raised over what the PM knew about Mr Raab’s behaviour before appointing him in his Cabinet.
Lib Dem spokeswoman for Health and Social Care Daisy Cooper said: "This Government hasn't got a shred of integrity left. Each day we see more chaos, more sleaze and more scandal.
"Steve Barclay now joins a long list of Conservative Ministers to have allegations made against them for inappropriate behaviour.
"These latest reports cannot be brushed under the carpet by Rishi Sunak - he must launch an investigation immediately. No staff should ever be subjected to working with or for a bully."
Mr Barclay is currently in a row with nurses after ministers this week confirmed it will take the Royal College of Nursing to court over planned strike action next month.
The RCN refutes a legal argument that its ballot does not give it a mandate to stage the planned walkout.
Pat Cullen, RCN General Secretary, has said: “Bullying nurses and dragging us through the highest courts would not be a good look for Government.
“It would show utter contempt for nursing staff. We will make the case for the legality of our action in all forums."
A Department of Health and Social Care spokesman said: “The department has not received any formal complaints relating to the behaviour of its ministers.
“Any complaints, relating to ministers or members of staff, would be investigated in line with departmental guidance.”
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