'Lives at risk' over 999 changes in mid and west Wales
Lives could be put at risk in rural areas because of changes to a first responder scheme in which fire crews help paramedics, claims a union leader.
Teams at 13 stations in mid and west Wales are trained to help with medical emergencies where they arrive first.
Adrian Hughes of the Retained Firefighters Union (RFU) warned of the risks to lives under the scaling back of the scheme.
The Welsh Ambulance Service said the scheme had not been abandoned.
Mr Hughes, the national officer of the RFU in Wales, said callout rates had dropped since May, and there had been "significant changes".
There are more fire than ambulance stations in mid and west Wales, and the fire service is seen as a quicker way of responding to certain medical emergencies.
The ambulance service pays the fire service for the role.
Mr Hughes said the fire crews used to respond to 115 different medical callout categories, such as chest pains and breathing difficulties, but the number had fallen to five which related to cardiac arrests.
"The firefighters that operate this service have been trained by the paramedics to ensure we can deliver the right level of service at the right level of skill, with the right equipment to help save lives," he said.
"We're not being used in a preventative way where we were before when somebody had quite bad chest pain, for example, and we delivered our usual skills and oxygen therapy and helped to stabilise the patient before the paramedics arrive.
Liberal Democrat AM Peter Black said the ambulance service had scaled back the scheme without proper consultation.
Asked on BBC Radio Wales what the impact could be in rural areas, he said there would be "greater call" on ambulance resources and the NHS.
He warned the entire scheme could "fall by the way side and people in rural areas will suffer".
"In many instances first responders perform first aid and reassure casualties, but that is not going to happen any more.
"This could put lives at risk," Mr Black said.
"Ambulance response times in rural areas are not going to improve because of the nature of the area, and this means patients will wait longer for basic first aid," he added.
A Welsh Ambulance Service spokesman said it could reassure the public the scheme "has not been abandoned".
"Fire service co-responders are still responding to cardiac arrests and other serious calls where they can provide a faster immediate response in conjunction with the ambulance service.
"Fire service and ambulance service managers will continue to liaise closely to ensure the effectiveness of this service," the spokesman added.
Siobhan McClelland, a lecturer in health policy and economics at the University of Glamorgan, said there had been issues about ambulance response times in rural areas where it was difficult to respond to emergencies quickly.
She said the fire service was used to respond in some cases where crews can react quicker to help and stabilise casualties.