The civil servant who alleges Gavin Williamson told them to “slit your throat” has made a formal complaint to parliament’s bullying watchdog.
The former chief whip is also alleged to have told them to “jump out of the window”.
The Ministry of Defence official said the behaviour had had an “extreme impact” on their mental health, they told Sky News.
They have reported Sir Gavin to the relatively new Independent Complaints and Grievance Scheme (ICGS).
It is the second complaint in a day, after a similar one by the former chief whip Wendy Morton.
It emerged at the weekend Sir Gavin claimed she had tried to “f*** us all over”, over the lack of an invitation to the Queen’s funeral.
The Conservative party has also launched a separate inquiry into the messages to Ms Morton.
Sir Gavin has rejected the suggestion that he bullied any staff, claiming that he had a “good working relationships” with his “brilliant” officials, although he has not denied using the words alleged.
Downing Street said the prime minister saw the claims, against one of his key allies, as “serious” and was considering further action.
It is believed this could include an investigation by the Cabinet Office’s propriety and ethics team into whether or not his behaviour would amount to a breach of the ministerial code.
His fellow cabinet minister Mel Stride also said it would be “utterly, utterly unacceptable” if the minister had told a senior civil servant to “slit your throat”.