Almost 60 consultants and senior doctors at Cheltenham General Hospital have said moving out-of-hours general surgery to Gloucester could put patients at risk.
They have written to Gloucestershire Hospitals NHS Foundation Trust's chief executive about their concerns.
The trust plans to move emergency and inpatient general surgery seven miles away to Gloucestershire Royal Hospital.
A spokesman said patients would have access to the correct care there.
One doctor, who asked to remain anonymous, told the BBC: "We can see a plane crash about to happen. It's going to be catastrophic.
"The trust doesn't realise the detail in their plan. It's not safe."
Cheltenham General is the only hospital in Gloucestershire treating urological, gynaecological and orthopaedic patients as well as providing chemotherapy cancer treatment.
Under the plans patients who develop internal bleeds, sepsis or abdominal pain overnight or at the weekend would have to be taken by ambulance to Gloucester.
Cheltenham MP Alex Chalk is against the trust's proposal and said he would raise the issue in Parliament.
He said: "I think it's an extremely bad idea, and more importantly we have this unprecedented situation where almost 60 medical professionals say it's a bad idea.
"This is nothing to do with money. This is about organisation and the key medical advice is that it's better to keep general surgery in Cheltenham to support other treatments."
A Gloucestershire Hospitals NHS Foundation Trust spokesman said the pilot reconfiguration would "improve patient care and safety as patients will have access to the right surgeon with the right expertise in Gloucester".
The spokesman added that general surgeons would be at Cheltenham during the day to carry out operations.
"In the rare event that a patient needs to be seen by a general surgeon out of hours - they may be taken by ambulance to Gloucestershire Royal."