Several people in Gordon Brown's office have contacted an anti-bullying charity, its boss has told the BBCBBC News - PM staff 'called bully helpline'
Christine Pratt said "three or four" calls had been made to the National Bullying Helpline in recent years.
Earlier Lord Mandelson denied claims Mr Brown had been warned about his temper, saying he "doesn't bully people".
Ms Pratt said she was not saying the PM was a bully, but said some of his staff "have concerns". Downing Street has yet to respond to the claims.
It follows a separate story in the Observer alleging that the head of the civil service Sir Gus O'Donnell was so concerned he had a word with Gordon Brown about his behaviour towards staff.
Time for Gordon Brown to go. He has done an excellent job keeping the UK economy through this terrible economic time and all Brits are probably richer for him, but he has lost the nations confidence and his presence makes it possible an utterly unfit toff could become the George W. Bush of the UK. I would hope to see Gordon gone by the end of this new week and Labour free to win this election.