Cuts in the health service are being introduced in a "haphazard" way which could harm patient care, the British Medical Association has said.
At the start of its annual conference, BMA chairman Dr Hamish Meldrum said it had received evidence of jobs being lost and access to services restricted.
The NHS is being asked to make savings because new treatments and an ageing population are raising costs.
The government says front line services must be protected as cuts are made.
Dr Meldrum, who was speaking at the start of the four-day annual doctor's conference which is being held in Brighton, accepted the NHS had to make savings.
But he said he was concerned about the way the early cuts were being introduced as doctors were not being consulted.
The NHS is one of the few areas of public spending which will not see its budget slashed in coming years.
But it is still being told to make savings because of the increase in pressure on funding from factors such as the ageing population, rising cost of drugs and obesity.
The BMA carried out a poll of more than 300 of its branches across the UK covering doctors who were involved in hospital, mental health and community services.
Only 92 medics responded - the low turnout was put down to the fact not many trusts had finished drawing up their plans - but the results still made worrying reading, the union said.
One in four doctors said their employer was planning redundancies and nearly two thirds reported freezes on recruitment.
Only a minority of these measures were being taken against doctors, with nurses and non-clinical staff bearing the brunt of the measures, the poll suggested.
However, the BMA said cuts to backroom roles such as administration still had an impact on doctors and nurses as they often had to pick up that work themselves.
Feedback also showed new services and facilities were being postponed or scrapped, while some GPs had reported tighter restrictions were being placed on which patients they could refer on for specialist treatment.
Some areas had also said existing services, such as treatment for varicose veins and blood testing, were being scaled back.
Dr Meldrum said: "Despite the government's best assurances that front-line services will be protected, our data show that cuts are already being planned or becoming a reality and that these will have an impact on doctors' ability to care for patients."
He urged NHS bosses to consult more with local people and staff about savings they had to make, saying in some places the decision-making seemed "haphazard" and "arbitrary" at the moment.
A Department of Health spokesman said: "Alongside all the public services, the NHS will need to deliver significant savings over the coming years.
"The department is very clear that savings should be implemented in a way that does not affect the quality of services and the secretary of state has been very clear that every penny saved will be reinvested back into patient care."