The Charity Commission has opened an inquiry into the National Bullying Helpline, it announced today.
A spokeswoman for the organisation, which regulates charities in England and Wales, said it had received 160 complaints about the helpline this week.
Its founder Christine Pratt provoked a political storm by claiming on Sunday it had received calls from Downing Street staff to seek help over alleged bullying at work.
The commission's spokeswoman said: "Concerns have been raised about the protection of confidential information held by the charity as a result of the operation of the charity's confidential helpline for victims of bullying.
"The commission has a statutory responsibility to promote public trust and confidence in charities, and is aware of the potential impact on other charities that run confidential helplines."
The inquiry will look at the helpline's procedures around data protection and examine how people were referred from the helpline to a business run by one of its trustees.
The helpline was temporarily suspended yesterday.
In a statement, the charity said it was considering its future and announced Mrs Pratt was "prepared to resign if necessary".
A number of the charity's patrons, including Conservative MP Ann Widdecombe, resigned in protest at what they saw as her breach of her duty of confidentiality towards callers.
In a statement on its website, the Helpline said: "Our patrons have resigned at a time when we needed them most. It is a shame that not one of them ever visited our charity offices to see how we operate or meet with our volunteers and trustees, despite request.
"Due to the situation at this time we are temporarily suspending our helpline. However, the website is still operational and contains practical, downloadable, documents for those who need it.
"Competitor anti bullying charities, individuals with an axe to grind and a few others have forced our hand. We are extremely sorry for any distress this may cause to those who need help right now. We apologise also to those who are detrimentally affected by this situation - we include all charities doing very good work across the UK."
The helpline repeated its assurance that it was "not politically driven in any way" and said its representatives would "be pleased to meet with Gordon Brown, to whom we wish no ill, if it would help to remedy the situation".
The statement added: "We are currently considering the future of the charity. Christine Pratt is prepared to resign if necessary. However, this will necessitate the appointment of a paid CEO which is a luxury we have not been able to afford in the past.
"We have very limited funds. Whatever happens, we will endeavour to act in the very best interests of the charity and all those who suffer from bullying and abuse of power - adults and children - everywhere.
"It was never our intention to cause hurt or distress to anyone when we set up a helpline."