HEALTH helpline NHS Direct is set to shut most of its call centres, including its base in Almondsbury, axing around 100 jobs in the village, according to union leaders.
Unison claims that 24 out of the 30 sites at the service have been earmarked for closure.
This means that around 50 per cent of the hotline's 1,500 nurses and other professionals could be made redundant.
A total of 100 staff work at the Almondsbury centre, which is one of the largest in the UK.
Yet, NHS Direct bosses have denied the allegations, saying they had not decided upon any closures and had only pinpointed which of its call centres would remain open over the next few months.
But Unison leaders said they were shocked by the scale of the possible job losses and warned that the move would be "disastrous" for patients and staff.
Michael Walker, Unison national officer for NHS Direct, urged the Secretary of State to save the health hotline.
He said: "The Secretary of State for Health should step in and stop this disaster immediately, we need action and we need it now.
"Axing dedicated hard-working nurses is never a good idea at any time, but this will directly impact on patient care. There is no doubt that patients will suffer as a result of this move. Unison is committed to working with management to minimise job loses and closures."
Every year, NHS Direct's nurses and healthcare professionals answer 4.2 million calls for medical advice and information.
Large centres in Sheffield, Wakefield, Nottingham, Hull, Stafford Chelmsford and Newcastle are among the 24 Unison claims will soon close.
NHS Direct bid for contracts across England to provide the NHS 111, a helpline aimed at patients who require medical help but do not need to call 999.
The organisation was successful and has now been awarded contracts to deliver NHS 111 services for 34 per cent of the population in England at just six of its 30 centres.
But Nick Chapman, NHS Direct Chief Executive, denied the union’s "unfounded" claims.
He said: "We have not confirmed that any sites are closing. At this stage we have confirmed which sites we will be keeping open to deliver NHS 111 in the areas where we have been commissioned to provide the service.
"Unison’s fears that 50 per cent of front line staff will lose their jobs are also unfounded. The future of other NHS Direct sites has not been decided. We are in discussion with the Department of Health and the NHS Commissioning Board about the future of other non-111 services that we could be asked to deliver before making decisions."
He added that, no matter bosses’ final decision for the remaining 24 sites, they would stay open until at the end of June 2013.