Patients who do not visit their GP for five years face being axed from their doctor's surgery under plans being rolled out across England.
Under the initiative, those who have not seen their GP for five years will be sent two letters asking them to respond.
Practice lists are being "cleansed" to remove so-called 'ghost' patients under an NHS initiative
If people cannot be contacted to say they still wish to be registered with their doctor, they will be removed from the practice list.
GPs are paid for every patient on their list - on average, they receive funding of about £136 per registered patient.
NHS England has employed private company Capita to lead the drive - known as "list cleansing" - to cut costs to the NHS and ensure accuracy over which patients use which services.
The idea is to find out whether patients no longer require services or have moved house, left the country or died.
But critics have warned that "ghost patients" are being removed inappropriately.
Pulse magazine, which published details of the plan, has carried out its own investigation which suggests thousands of "ghost patients" have been inappropriately removed from practice lists in recent years.
GP leaders also told Pulse that the scheme could result in patients missing out on vital appointments or health checks.
Pulse has seen the Capita contract with NHS England. It states: "The supplier shall contact all GP practices in the eleventh month of every contract year requesting a list of all patients who are recorded as not having had contact with the GP practice in the past five years."
Capita will then contact each patient "within 10 working days" to confirm their "current address and registration details". If they do not respond, then the patient's record will be flagged for removal within six months.
Dr Robert Morley, from the British Medical Association (BMA), said: 'Patients have a right to be registered unless they move or register elsewhere, even if they don't need to or choose not to access services.
An NHS England spokeswoman said: "The National Audit Office and House of Commons Public Accounts Committee have all drawn attention to the need to ensure accurate patient lists, and for proper stewardship of public funds. We doubt that contractual change would be needed but, should it be, we will cross that bridge when we come to it.""NHS England should abandon this exercise which will have the inevitable consequences of disruption for patients and a reduction of core funding disproportionately impacting the most vulnerable practices."
It said any patient who has their registration cancelled would need to be re-registered on contacting their surgery.
Katherine Murphy, from the Patients Association said: "If the NHS insists on proceeding with this plan, despite our previous warnings, then it needs to do so with extreme caution.
"Some patients may struggle to understand or get confused as to why they are being asked to confirm their details, and others could simply overlook it.
"Ultimately, in both of these circumstances, people will wrongly be taken off the list and may not realise it until it is too late and they urgently need to see their GP.
"Moreover, when undertaking such a vast project like this, it is plausible that a patient could be removed in error. But taking the wrong person off the list could have could have a serious impact on patient safety."