Wokingham ambulance call centre to merge with Bicester
A 999 call centre in Berkshire is moving to its Oxfordshire HQ more than 50 miles (80km) away.
Workers at Wokingham will need to relocate to the South Central Ambulance Service (SCAS) HQ in Bicester in July.
A Unison spokesman said staff without local knowledge would compromise "patient safety" and added that employees were "concerned".
SCAS operations manager John Nichols said it was important that calls were "answered quickly".
South Central Ambulance Service NHS Trust has emergency operations centres in Wokingham, Bicester and Winchester.
Mr Nichols said the merge of three of its centres to two was a trend among many ambulance services to improve efficiency.
Unison spokesman Darren Tomkins said the union was "disappointed" it was not consulted on the merger, which affects more than 50 workers at Wokingham.
He added the loss of local knowledge in Berkshire may lead to an increase in response times.