The Royal College of Nursing was last night heading for its first industrial action after staff at the John Radcliffe hospital in Oxford said overcrowding of the accident and emergency department was putting patients' lives at risk.

A union committee agreed to recommend a ballot of the 70 nurses working in the unit. Industrial action could include working to rule, a ban on overtime or refusing to treat patients in places nurses consider unsuitable.

The full RCN council is expected to support the proposal within the next 10 days. If the hospital does not move quickly to solve the problem, it could be the first to be targeted since the RCN changed its rules in 1995 to permit limited industrial action that did not affect patient care.

Patricia Marquis, the union's regional officer, said: "For several years, conditions have become more and more difficult [at John Radcliffe]. There have been increasing numbers of patients and, partly because of the nurse shortages, fewer beds."

It was common for every corridor to be full of people waiting on trolleys, but the overcrowding reached crisis proportions 10 days ago when the unit held three times the approved maximum number of patients. "This means the nurses cannot give patients the best care, or even privacy and dignity, and safety is being compromised."

Last year the nurses made a formal complaint to the trust management and a panel upheld their complaints, Ms Marquis said. But an action plan was not fully implemented and problems continued. "The nurses are at the end of their tether and now feel this ballot is their only course," Ms Marquis said.

David Highton, the hospital's chief executive, said: "I understand the frustrations of our accident and emergency staff and am deeply concerned about the difficulties they face.

"It is no great secret that the emergency care system in Oxfordshire has been very stretched recently.

"I will continue to talk to the RCN and to our own staff about how we can work together to relieve some of the pressures and improve the system as a whole."

The hospital serves more than 600,000 people in the Oxford area. A report last year on its heart unit criticised a "culture of cronyism" that left the centre in chaos. Personality clashes between doctors left the unit "on its knees" and threatened its future, the report said.