Five further complaints about Dominic Raab's behaviour as a minister are being investigated, No 10 has said.
The prime minister's official spokesman said the claims related to Mr Raab's previous tenure as justice secretary.
It means a total of eight complaints are now being investigated by senior lawyer Adam Tolley KC.
Mr Raab, who was reappointed by Rishi Sunak as justice secretary and deputy prime minister in October, has denied allegations of bullying.
Appearing in front of Parliament's Joint Human Rights Committee on Wednesday, Mr Raab said he had "behaved professionally throughout".
He told MPs he welcomed the investigation so he could deal with claims "transparently", rather than through "tittle tattle that's anonymously leaked to the media".
The MP for Esher and Walton previously served as justice secretary and deputy prime minister under Boris Johnson.
A close ally of Mr Sunak, Mr Raab was sacked from those roles when Liz Truss became prime minister in September.
The three complaints already under investigation related to his time as foreign secretary and Brexit secretary, as well as at the Ministry of Justice.
A spokesman for Labour leader Sir Keir Starmer said it was "pretty shocking" that no action had been taken against Mr Raab and called for him to be suspended.
He said it was "a consequence of having a weak prime minister" that Mr Raab...
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