Islington residents are being urged to consider opting out of NHS Digital plans that could see their data collected.
Patients have until June 23 to inform their practice that they do not want their medical histories adding to a national database.
London Assembly Member Sem Moema is looking to publicise the move to her Islington constituents, saying "it could take a lot of people by surprise".
Labour has raised concerns that this could lead to sensitive information being shared with third parties, although the NHS has said there will be barriers between records and researchers.
Ms Moema said: “We are talking about the collection of very sensitive information and unless we see the public messaging ramped-up and the deadline for opting out pushed back, this is going to take a lot of people in our borough by complete surprise.
“We need to make sure that the centuries old understanding around patient-doctor confidentiality is upheld, so the government has to be totally transparent in what they’re doing here and set out how they are going to protect this data.”
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