Northamptonshire Labour wants plans to store increased amounts of patient data within the NHS to be scrapped.
The NHS care.data programme will bring together data from the records of GPs and hospitals on to a central computer system.
NHS England says the initiative will ensure healthcare can be improved by tracking more comprehensively which treatments are the most effective for patients.
But Cllr Eileen Hales, the shadow member for public health and wellbeing at Northamptonshire County Council, says she is concerned about where patient data may end up and that the database may become a “market place for private health companies”.
She said: “The real concern here is that the new database seems to be being pushed through on the quiet with the majority of people knowing nothing about the scheme.
“I am worried about who will be able to access this information and the possibility of future expansion of the system to potentially allow private companies to monetise the health service.”
Labour colleague Cllr Mary Butcher said she feared the changes could accelerate what Labour has described as the privatisation of the NHS.
Cllr Butcher added: “People are not aware just how much is changing within the NHS, and how quickly and quietly it is being pushed through.
“If we are not careful, we will end up with an NHS that is fully privatised and there will be no free health care.
“That is certainly the direction of travel under this Government, and we must fight it.”
NHS England announced in the autumn that all 22 million households in England would receive a leaflet in January explaining what it describes as the benefits of the new system.
At that time Tim Kelsey, NHS England’s director of patients and information, said: “At the moment, the NHS often doesn’t have the complete picture as information lies in different parts of the health services and isn’t joined up.
“This programme will give NHS commissioners a more complete picture of the safety and quality of services in their local area which will lead to improvements to patient outcomes.”