Christine Pratt's charity helpline has been under intense scrutiny
The Charity Commission is investigating the charity at the centre of a row over claims of bullying at Downing Street.
It said it had received more than 160 complaints about the National Bullying Helpline and had moved to prevent any more details of calls being disclosed.
Helpline chief executive Christine Pratt was criticised for saying it had been contacted by Downing Street staff amid claims about the PM's behaviour.
The helpline was suspended on Wednesday while the service considers its future.
Mrs Pratt spoke out last weekend following allegations in a book about Gordon Brown's temper and behaviour towards staff.
The Charity Commission said it had a duty to "promote public trust and confidence in charities, and is aware of the potential impact on other charities that run confidential help lines".
It said it would "ensure the trustees continue to protect this confidential and sensitive information" and had made an order "preventing the transmission or disclosure of information, including details about the nature and source of the confidential calls it has received" without its permission.
BBC political correspondent Iain Watson said it meant the commission was taking steps to prevent Mrs Pratt from accessing information that could back up her claims.
On Tuesday, the publicist Max Clifford said he had spoken to Mrs Pratt and told her she needed to provide evidence of her allegations.
After she went public on Sunday, all four of the charity's patrons resigned and, along with another bullying charity, strongly criticised Mrs Pratt for what they called a breach of confidentiality.
'Prepared to resign'
She said she had not named names or revealed details and also stressed she was not calling Mr Brown a bully or saying the calls they had received concerned him personally.
The National Bullying Helpline was temporarily suspended on Wednesday, saying it was considering its future and Mrs Pratt was "prepared to resign if necessary".
The row began on Sunday with a story in the Observer - based on a book by journalist Andrew Rawnsley - alleging that Mr Brown grabbed staff by the lapels, shoved them aside and shouted at them.
Business Secretary Lord Mandelson denied the claims, insisting the PM was "demanding" but "doesn't bully people".
But Mrs Pratt then contacted the BBC to say a flat denial sent out the wrong message and she would expect Downing Street to follow "due process" and look into calls that her helpline had taken from a small number of staff.
'No pep talk'
The government has denied allegations in Mr Rawnsley's book that the head of the civil service, Sir Gus O'Donnell, had a "pep talk" with Mr Brown about his behaviour towards staff following reports some were frightened by his temper.
Sir Gus said on Wednesday he had spoken to the PM about how to motivate staff but denied talking to him about his "behaviour".
Speaking on BBC One's Question Time on Thursday, Welsh Secretary Peter Hain defended Mr Brown saying: "He's had women and other members of staff working for him for years, in one case over 20 years - these are not people who would do that if they thought he was a bully. Of course they wouldn't."