Nurses are to stage a summer of protests across the UK after a poll showed strong support for strikes over pay.
The Royal College of Nursing warned that unless the next Government drops the 1% cap on pay it will hold a ballot on industrial action later this year, threatening the first ever strikes by its members.
The RCN said nurses voted in a consultative ballot by nine out of 10 to support action short of a strike while almost four out of five backed strikes.
More than 50,000 of the RCN'S 270,000 members took part in the poll. Another ballot would have to be held before any action takes place.
The RCN has warned that low levels of pay are partly responsible for tens of thousands of unfilled nursing posts.
Nurses have suffered a 14% pay cut in real terms since 2010 because of a government cap on public sector pay, said the RCN. A formal pay cap of 1% was introduced in 2015.
Michael Brown, chairman of the RCN Council, said: "Our members have given us the very clear message that they can't and won't take any more.
"This is an unprecedented show of anger and frustration over the Government's pay policy. Politicians must now listen and tell us what they will do about nursing pay.
"It's a message to all parties that the crisis in nursing recruitment must be put centre stage in this election. We're demanding answers on behalf of our patients as well as nursing staff.
"If we don't stand up now, how can we guarantee their future safety and wellbeing?
"The RCN has never gone on strike before, so balloting our members would be a very significant step.
"We've heard from members that they want to send a much tougher message to government which is why we will be leading them in a summer of protest activity.
"They have been clear that if the next Government doesn't respond and lift the unreasonable cap on nursing pay, they want us to ballot on industrial action.
"It would be the first time RCN members came out and took industrial action in our 100 year history."
Janet Davies, general secretary of the RCN, said: "What's happened today is unprecedented for the RCN and is a reflection of the deep anger members feel.
"The current conditions in the NHS are driving people out of the profession and putting new people off entering it.
"Our argument is not with patients - this is about ensuring that they get the safe and effective care they need. The 1% cap on nursing pay is putting patient care at risk.
"It's not just the RCN saying this - we heard from NHS trust leaders last week that if nursing staff aren't paid a proper wage, they won't be able to keep patients safe.
"The next Government must tell us what they're going to do about nursing pay to stop the nurse staffing crisis."
Jon Skewes, director of policy at the Royal College of Midwives, said: "NHS staff have now seen seven years of pay restraint and with at least another three years on the horizon.
"Continuing pay restraint is a disastrous, unsustainable policy for maternity services and the NHS. We are working with other NHS trade unions to break the Government's policy of pay restraint."
Dr Mark Porter, British Medical Association council chair, said: "Year after year of real-terms pay cuts have had a damaging impact on the morale of frontline NHS staff.
"Ongoing pay restraint has seen doctors' pay fall by up to 17% in recent years, leading to staff shortages and impacting on patient care, and doctors across the country will agree with the very strong message sent today by nurses, that the pay cap is unfair, unacceptable and must be lifted."
A Tory spokesman said: "Our nurses do a fantastic job.
"We've had to take difficult decisions on pay across the public sector given the deficit we inherited - while continuing to boost the NHS budget so patients get high-quality care.
"We've prioritised increasing the number of nurses to help those already working hard - with 12,100 more on our wards since 2010.
"But in truth, the only way we can increase NHS funding, staffing or pay is to get a good Brexit deal so the economy prospers in the years ahead – and only the strong and stable leadership of Theresa May can deliver that."
Scottish Labour Health spokesperson Anas Sarwar MSP said: "Our NHS nurses are the foundation of our health service, but as this report shows they aren't getting the support and the resources they need from the SNP government.
"In fact, nurses in our health service have faced on average a real terms cut of £3,400 as a result of Nicola Sturgeon's pay cap."