The Government will have access to data from individual GP practices on how many "fit notes" are issued for patients.
From next month, the Department for Work and Pensions (DWP) will be able to see information extracted from GP records, including the number of fit notes issued by each practice and the number of patients recorded as "unfit" or "maybe fit" for work.
It has previously said the data will be published anonymously at Clinical Commissioning Group (CCG) level but an investigation by Pulse magazine has found that DWP officials will be able to look at the data for individual GP practices. It will also be able to share this data with other bodies.
The data will include how many computer-generated fit notes are issued, how many patients are recorded as unfit or maybe fit for work, the duration of the fit note and the gender of the person the fit note was issued for.
The data will also say what type of health condition the person has and the location of where the note was issued.
A DWP spokesman said: "We know the damage that can be done when people are absent from the workplace for extended periods of time, that's why we want to ensure that people get the best possible support to return to work – or to avoid falling out of work in the first place.
"All fit note statistics are anonymous, and they will help provide a better understanding of why people take sickness absence in different areas across the country, so we can make the service as effective as possible for businesses and employees."
Some of the data is due to be published by the Health and Social Care Information Centre (HSCIC) in the spring.
GPs will need to inform patients their data is being taken, but cannot withhold information unless their patient explicitly objects.
The DWP told Pulse no practice-level information would be shared outside the department, with a spokesman saying: "Only the Department for Work and Pensions will be able to access the data at GP practice level."
Family Doctor Association chairman Dr Peter Swinyard told Pulse: "I think that is state snooping.
"Although I am sure some civil servant thought it was a terrific idea somewhere, I am not entirely sure I agree. I don't know if patients understand that when I write a fit note, some bureaucrat is going to be able to have a look at it."
GP and data sharing campaigner Dr Neil Bhatia said he was "not sure why" practice-level data was required, "other than to compare practices, create league tables, name and shame".
He added: "I think it would be extremely difficult to make sense of the information out of context of the consultation."