Paramedics on emergency callouts in the Bristol area have had to phone 999 to demand back-up.
Workers are angry that a hotline to their control room has been scrapped.
This served paramedics who drive estate cars, which carry lifesaving equipment and can reach incidents faster than ambulances.
These paramedics work alone.
Ambulance workers in the Unison union and the Association of Professional Ambulance Personnel are now considering industrial action because of their safety fears for paramedics working alone.
Since the hotline was merged with their control centre’s main dispatch desk in May, paramedics have had difficulties getting through to the control room.
The union reports that at least six paramedics have had to ring 999 to try to speak to the dispatch team.