Emergency services at Belfast's Royal Victoria Hospital face temporary closure after staff were attacked by individuals claiming to be members of the Loyalist Volunteer Force, a union warned last night.
The Northern Ireland public service union UNISON said staff were afraid to return to work following the incident, which occurred early on Saturday morning.
The RUC was called to the west Belfast hospital after workers were assaulted, had their lives threatened and were spat upon. Police are studying video footage of the attack.
Some staff feared for their lives and were reluctant to go back to work, a UNISON spokeswoman, Ms Patricia McKeown, said.
"We may be facing the closure of the largest trauma centre in Northern Ireland and that is not an acceptable situation,' she said.
Hospital management condemned the incident and called on influential members of the loyalist community to personally intervene.
The hospital's medical director, Dr Ian Carson, described the attack as "deplorable".
"It is intolerable that people purporting to have interests in patients receiving crucial care, should subject staff to physical and verbal abuse and threaten their lives."
"This disgraceful behaviour must stop immediately and be condemned by all, especially those who would have influence in the group to which these people claim to belong."
The Northern Ireland health minister, Ms Bairbre de Brun, condemned the "disgraceful scenes".
The threats are similar to those experienced by staff in the Mater Hospital in north Belfast in February, when the UDA was blamed.