Patients with diabetes are missing out on vital prescriptions that let them keep tabs on their condition, despite repeated warnings, says Diabetes UK.
Its poll of 1,300 patients found nearly half had had prescriptions for blood-testing strips refused or restricted.
The Department of Health has previously written to GPs reminding them not to restrict access to this kit other than for clinical reasons.
Doctors say there is a balance to be struck with protecting NHS resources.
Diabetics must know their blood-sugar reading to stop it going dangerously high or low.
In the long-term, poorly managed blood-glucose levels can lead to serious complications such as blindness, amputations and stroke.
Although type 2 diabetes can sometimes be managed by keeping a close check on what you eat, type 1 needs a medication called insulin to keep blood glucose in a safe range and so requires frequent blood sugar tests.
Cost v benefit
In the poll by Diabetes UK, 39% of those who had experienced restrictions to blood-testing strips had type 1 diabetes.
While the survey may not be representative of all people with the condition, Diabetes UK says it shows that GPs restricting test strips is a significant issue.
Chief executive Barbara Young said GPs seemed to be restricting access to strips to save money.
"But any short term savings from doing this will be tiny compared to the long-term cost to the NHS of treating these complications," she said.
"We need to send an urgent message to NHS England that GPs restricting access to strips on cost grounds is wrong-headed, short-sighted and unfair. It has to stop."
Dr Steve Kell, co-chairman of NHS Clinical Commissioners, which represents over 85% of Clinical Commissioning Groups, said: "Prescribing decisions should be made on the basis of clinical need and cost-effectiveness, not cost alone.
"Patients with diabetes should receive a review at least annually to ensure that they are receiving the appropriate treatment and that all prescriptions are suitable.
"There has been significant over-testing and over-prescribing of strips in the past for some patients, and this is not beneficial for the patient or the NHS."