Plans to cut up to 1,000 jobs at an NHS trust in Greater Manchester will have an impact on patients, the British Medical Association (BMA) has said.
The Pennine Acute Trust, which runs hospitals in Oldham, Bury, Rochdale and north Manchester, expects to have to save at least £45m by April 2012.
Its chief executive John Saxby said the savings could mean losing 10% of jobs.
Dr JS Bamrah, of the BMA, said: "You simply cannot provide the same level of service with 10% fewer staff."
'Undoubtedly be impact'
Mr Saxby said he estimated the trust would have to save £45m, as part of the wider NHS having to find efficiency savings of £20bn.
This could rise once the trust knows what services GPs want to commission, Mr Saxby believes.
He said the savings could not be met by cutting waste or reducing non-pay expenditure and all areas of the trust needed to be looked at to "reduce costs and work more efficiently".
As 70% of the trust's budget is spent on wages, up to 1,000 jobs from a total of 10,000 may have to be cut, he said.
Dr JS Bamrah, chairman of the BMA's North West regional council, said: "We don't yet know the detail of which posts will go, but there will undoubtedly be an impact on patients.
"You simply cannot provide the same level of service with 10% fewer staff, even if they are in non-clinical roles."
Labour MP Simon Danczuk, whose Rochdale constituency is served by Pennine Acute Trust, said the job cuts would affect both patients and the local economy.
"It is going to have an adverse affect on services people have in hospital, and on the wider community.
"Public sector jobs are very important in Rochdale. These cuts will inevitably have an effect on the local economy.
He added: "The Conservatives said in the run up to the general election they were going to cut the deficit but not the NHS.
"This latest reduction in the number of jobs in the NHS is more proof they are cutting the NHS."
A Department of Health spokeswoman said: "The government promised to reduce NHS bureaucracy and plough this money straight back into patient care, and that is exactly what we are delivering.
"Since May 2010, we have thousands more doctors, nurses and midwives - and 2,000 fewer managers.
"Labour oppose these cuts in bureaucracy, just as they oppose our investment in the NHS and our modernisation plans. They would spend less and do nothing."
The Pennine Acute Trust, which serves a population of 800,000, said it hoped compulsory redundancies would not be necessary.