Tensions between Catholic and Protestant workers in the Mater Hospital in north Belfast are so high that the Irish Congress of Trade Unions' anti-sectarian unit, Counteract, is to be brought in to ease the situation.
Ms Patricia McKeown, regional secretary of the public sector workers' union, Unison, said sectarian tensions between the two communities on local streets had spilled over into the hospital.
Unison has held a series of meetings with the Mater Hospital Trust and has asked management to co-operate with the unions to sort out the difficulties, she said.
Tensions within the hospital are long-running. Loyalist paramilitary death threats were issued against some Catholic staff 13 months ago. However, sources said the situation deteriorated further in September when Protestant residents of Glenbryn restarted their protest at Holy Cross girls' school in Ardoyne. Glenbryn residents and Holy Cross parents are both employed in the hospital.
It is understood that while there have been no violent incidents, groups of workers are refusing to speak and co-operate with each other. "They are boycotting each other and the situation is intolerable," said one Unison member.
Sources said a group of Protestant workers in the Mater had recently left Unison. Ms McKeown confirmed that 12 Unison members had left. "It is inevitable that problems on the streets will manifest themselves in the workplace too. The Mater Hospital is the biggest cross-community employer in north Belfast.
"Feelings have been running high. There are very real differences between workers. People aren't talking to each other in the workplace, rumours are circulating and things are getting blown out of proportion. It's unacceptable and we must deal with it.
"We have talked to the Mater Hospital Trust and we plan to bring in Counteract, ICTU's anti-sectarian unit. We have to address these tensions head on. Otherwise, they could lead to intimidation, bullying and harassment," said Ms McKeown.