In an online poll of 1,500 nurses, midwives and healthcare assistants, respondents said they feared care is so poor a Mid Staffordshire scandal could happen again.
The research found 60% of staff did not have enough time to deliver safe and compassionate care. It also found 45% of respondents were looking after eight or more patients on their shift.
The research asked respondents how confident they were that a similar situation to Mid Staffs could never happen at their NHS trust: 35.7% said they were either very (6.2%) or fairly (29.5%) confident it would not happen. But 29.6% said their trust was at risk of a Mid Staffs-type situation, while 9.9% said that was already happening in the hospital and 9.8% said it was already occurring across the organisation.
Minimum staff-to-patient ratios could dramatically change life on the wards for patients and staff, providing a safer, more caring environment for everyone, Unison claims.
Christina McAnea, Unison head of health, said: "This survey exposes a health service under severe strain. On this typical day many staff worked through their break and stayed after their shift – but this still did not give them enough time to complete all their tasks.
"The hidden voice in the survey must surely be that of the patient who is not getting the level of care they are entitled to expect.
"Government cuts are making matters worse by reducing staff, including nurses, at a time when patient demand is growing.
"Introducing minimum nurse-to-patient ratios would provide a safety net of care, restore public confidence and show nursing staff they are respected and valued."
However, the NHS Employers organisation has responded to the survey by saying introducing minimum staffing levels would limit how hospitals could plan resources in a way that's best for their patients.
Sue Covill, director of employment services at the NHS Employers organisation, said: "Getting care right all the time is what we strive for and this means matching the skills of staff to the needs of patients, within a culture of compassion and diligence. The best decisions can only be made by looking at the healthcare team as a whole, which means addressing the balance between nurses, doctors, support staff and many others.
"We are pleased that the Government's response to the Francis report supports our view that it is local NHS organisations which are best placed to take responsibility for minimum staffing levels and skill mix.
"And we would support the further development of the evidence base for making decisions about safe staffing levels which is being developed by the National Institute for Health and Care Excellence (NICE)."