GPs in south east Wales have been told not to write letters in support of patient's benefit claims, as it is an "abuse of NHS resources".
Recent changes to the way people are assessed as being able to work have led to an increasing number of people turning to their GPs for letters supporting their claims.
But the Bro Taf local medical committee (LMC), which represents GPs in the region, has sent a letter to local surgeries, saying: "GPs have a contract with the NHS to provide general medical services to their patients and are not in a position to administer or police the benefits system.
"GPs are not contracted or resourced to provide this kind of service and making such requests to GPs represents an abuse of NHS resources.
"We cannot therefore respond to your request for a letter."
Disability Wales has branded the policy as "almost callous".
Speaking to BBC Radio Wales, LMC chair Dr Charles Allanby said that the increase in patients asking for letters was adding to GP workloads.
"We are seeing at least one or two patients per surgery per doctor, asking for assistance," he said.
"If you add that up throughout the whole of Wales, that is an enormous number of appointments being taken up by people who are not actually ill.
"Do we want to see doctors seeing ill patients, or do we want to see doctors seeing patients who are not ill but simply want to undertake some form of appeal letter?"
A spokesperson for the Department for Work and Pensions (DWP) said that GP letters were a standard part of the system by which claimants are assessed.
"A decision on whether someone is well enough to work is taken following a thorough assessment and after careful consideration of all the available evidence.
"That can include supporting medical evidence from the claimant's GP or other healthcare professional."