Four of the country's biggest charities are being investigated amid claims fundraisers contacted people on the Government's "opt-out" database.
The NSPCC, British Red Cross, Oxfam and Macmillan Cancer Support have been accused of making fundraising calls to people registered with the Telephone Preference Service (TPS), which protects them from receiving unsolicited sales or marketing calls.
The accusations have been made after an undercover reporter with the Daily Mail worked in a call centre fundraising on behalf of the charities.
The Mail said charities were prepared to take money over the phone from people with dementia, Alzheimer's disease and memory problems.
The charities tonight said they were aware of the allegations.
It comes following the death of 92-year-old poppy seller Olive Cooke, who apparently killed herself shortly after being overwhelmed by requests from charities.
A spokesman for the Information Commissioner's Office (ICO), responsible for enforcing data protection laws, said of the Mail's investigation: " We're aware of allegations raised against several charities, and will be investigating whether there have been any breaches of the Data Protection Act or Privacy and Electronic Communication Regulations."
An undercover reporter for the Mail spent three weeks carrying out fundraising campaigns on behalf of Britain's biggest charities at a call centre called GoGen in East London.
Those with dementia and Alzheimer's are allegedly being treated as legitimate targets - as long as they agree to the call and are able to answer a few basic questions over the phone, the newspaper reported.
In a statement, GoGen said they refuted "many of the claims" and said they " do not make cold calls of any kind to TPS registered data supplied by third parties generated by lifestyle or profiled survey questionnaires".
The spokesman said the company has consulted with the fundraising regulator and "agreed to have the FRSB conduct a thorough investigation into these allegations".
Tim Hunter, Oxfam's fundraising director, said: " Oxfam supports more than 11 million people worldwide thanks to the help of the British public - we only contact those people who have expressed an interest in receiving a call.
"I have personally tested the robust measures in place to ensure these standards are maintained and vulnerable people are protected. We monitor calls, carry out undercover spot checks and work with the industry watchdog to make sure our strict guidelines are followed.
"Any potential supporters of the Engage Campaign who are on the Telephone Preference Service are only contacted if they have given us their explicit consent. At this time there is no primary evidence to suggest this is not the case."
A Macmillan spokeswoman said: "We take the claims made by the Daily Mail seriously and are looking into these as a priority.
"We do not wish to contact people if we are aware this is unwanted. We take the requests of our supporters very seriously and all supporters can choose to unsubscribe from communications at any time.
"We would not hesitate to take robust action if we found our agencies were not acting with utmost integrity on our behalf."
An NSPCC spokesman said: "We have clear contractual arrangements in place with those that fundraise on our behalf, including strict guidance on vulnerable people, and expect the highest standards of behaviour from everyone who operates under the NSPCC banner.
"We regularly review the companies we use and will take breaches of those standards extremely seriously.
"Any suggestion of inappropriate activity is deeply worrying and we would want any concerns to be raised with us immediately so that they can be quickly addressed."
A British Red Cross spokeswoman said: "The British Red Cross will not tolerate lapses in maintaining the highest standards to protect vulnerable people.
"We would never knowingly ask for donations from someone with Alzheimer's or dementia and further measures are being put in place to ensure best practice is followed at all times.
"We will fully cooperate with any investigation by the ICO."