Endoscopy allows doctors to look into the stomach
New guidelines that restrict which patients GPs can refer to hospital will mean cancers are missed, warn doctors.
By sending only patients with the most worrying symptoms of indigestion for checks on the gullet, cancer may be too advanced to treat, they say.
Surgeons are advising doctors to ignore the National Institute for Clinical Excellence's advice and continue to refer whenever in doubt.
NICE stood by its guidance, saying it took account of all available evidence.
The watchdog says routine endoscopy - where a small camera is put down into the gullet - is not necessary for any patients unless there are "alarm" signs, such as bleeding.
These signs mean the patient should be referred urgently to be examined by a specialist within two weeks.
If the patient is aged 55 or older and their indigestion does not go away with medical treatment, such as drugs that lower stomach acid, GPs should consider referring them for endoscopy.
Patients who have had a stomach ulcer in the past or surgery for a stomach ulcer, who are taking aspirin-type drugs that can be damaging to the stomach lining, or who are at increased risk of stomach cancer or anxious about cancer can also be referred, it says.
Bleeding or anaemia
Unexplained weight loss
Progressive difficulty swallowing
Swelling of the upper abdomen on examination
But the Association of Upper Gastrointestinal Surgeons of Great Britain and Ireland says even with these caveats, the boat is being missed, and waiting too long could put lives at risk.
Professor Michael Griffin, president of the association, said: "If these guidelines are adhered to it will mean the only patients we pick up will be those we cannot cure.
"By waiting, early cancers will not be picked up and treated."
He said the guidelines also undervalued endoscopy for diagnosing other serious and painful gut problems, including ulcers.
"It's also important because a normal result is reassuring both for the doctor and patient," he said.
He said the evidence assessed by the guideline committee was incomplete and that the committee had failed to consult with the surgeons who treat upper gastrointestinal cancers.
He was also concerned that the measures were a way of saving money to divert to other NHS services.
A spokesman from NICE said: "The NICE guideline development group considered all the available evidence and consulted widely with groups representing health professionals and patients involved in this area before making its recommendations."
Dr Graham Archard, vice chair of the Royal College of GPs, said: "Delays in referrals can, in some cases, result in serious problems going undetected and ultimately cost lives.
"We would urge GPs to be vigilant and if in doubt always refer."