Patient care is being "jeopardised" by the amount of pressure that is being put on nurses, a new report suggests.
UK patients are being put at risk because of nursing staff cuts and excessive workloads, the Royal College of Nursing (RCN) said.
The union said there is"unprecedented" stress on nurses which is leading to many of them suffering from ill health.
Indeed a poll conducted by the RCN on 2,000 nurses working across the NHS and private sector found that m ore than half have been made unwell by stress in the last year.
And four in five of said they have battled through feeling unwell and still gone into work.
The RCN said that m any nurses questioned reported that sickness absence policies at their place of work were so punitive that they had no alternative but to attend work despite feeling unwell.
One of the nurses questioned told the RCN: "I've been told that if I don't meet the 100% attendance at work I will be up for a capability hearing. I had three admissions into hospital due to a cardiac problem, so if I get chest pain I have to ignore it because I have to go to work."
Another said: "I am currently off work following breast cancer, a senior manager called three weeks after my surgery and asked if I was coming back as people with cancer often don't return and they wanted to fill my post."
The union said that if nurses are going into work feeling unwell patient safety could be in jeopardy.
RCN officials also raised concerns about working culture for nurses after 56% said they had experienced physical or verbal violence from patients in the last year and almost a quarter (23%) reported being bullied by their managers,
Dr Peter Carter, general secretary of the RCN, said: "In the aftermath of the Francis Inquiry, it is clearer than ever that working cultures in the NHS and beyond have a direct and serious effect on the level of care that staff can provide to patients.
"Our whole care system is currently facing the huge challenge of delivering care at a time of increased demand and scant resource. This is the reality which nurses face in every working day.
"There is much that managers and employers can do, and should be doing, to support staff and keep patients safe. By ensuring there are enough staff to deliver care, and enabling staff to raise concerns safely, the positive working culture which exists in many places could be the reality everywhere.
"Worryingly, this report shows that rather than an environment which supports staff, some employers are instead adopting panic behaviours. Staff report being intimidated and blamed, and feel they have no way of speaking out about threats to patient care. Individual nurses are clearly going the extra mile to make sure the job is done, however, the risk of burnout is very real, and very widespread."
A Department of Health spokeswoman said: "The staff working for our NHS are our health service's most precious resource. Nurses are working extremely hard and continue to provide a high quality of care in the face of rising healthcare demands. We want to support nurses as much as possible and are already investing in technology and training, while looking at cutting bureaucracy by a third to allow nurses to focus on patients and not paperwork.
"Recent reports have shown clearly that we need safe numbers on wards and a supportive culture in the NHS. We have already introduced some major changes, such as a Chief Inspector who will take action on staffing levels."