Up to 1,000 nursing posts in England could be lost as NHS bosses struggle to balance their books, nurse leaders say.
One in four NHS trusts had a deficit last year
Some trusts have already announced recruitment freezes, but the evidence from the Royal College of Nursing shows the problems are more widespread.
The RCN said patient care would suffer if nurses lost their jobs or vacant posts were not filled after one in four trusts finished last year in deficit.
But the government said there was no evidence of redundancies.
NHS trusts in south London and Portsmouth have already announced recruitment freezes for a variety of posts, including nurses, and an Oxfordshire trust is considering cutting 14 doctor posts.
But the RCN, which gathered evidence from its members, said the situation could be far worse.
Officials said 3,000 posts could be lost - either through redundancies or recruitment freezes - including 1,000 nurses. The others are expected to come mainly from admin and support areas.
Nurses of all grades, including specialist nurses and modern matrons could be hit, the RCN said.
One trust, the Leeds Teaching Hospitals NHS Trust, is considering scrapping up to 600 posts - 4% of its workforce - some of which will be nursing positions.
RCN general secretary Beverly Malone said: "We are putting a spotlight on this issue now before it is too late.
"Valuable, highly experienced staff could be lost and we simply cannot afford to let this happen.
"It will hit patient services and put even more pressure on the nurses that are left."
Shadow Health Secretary Andrew Lansley said frontline staff were "bearing the brunt of the government's financial mismanagement in the NHS".
"It is a disgrace that highly valued nurses are not getting jobs and some are being made redundant."
A spokeswoman for the NHS Confederation admitted some trusts were having to consider redundancies.
She added: "Trusts will take every step to ensure there is no impact on patient care and they will always examine other options that they can take to improve their financial position."
But Health Minister Lord Warner said: "We refute this claim. Overall, our figures suggest that the NHS is actually planning to increase the number of nurses this year by 2%.
"We have received no evidence that trusts are planning to make actual redundancies amongst the senior nurse workforce, though a number of trusts are choosing to close posts when the incumbent retires."