Scottish Ambulance Service is proposing to reduce its control rooms from eight to two or three.
The plans emerged following a review conducted as part of the wider Beyond 2000 review of ambulance services in Scotland, prompted by reports from the National Audit Office and the Audit Committee of the Scottish Parliament. Both identified a number of areas for improvement.
Scottish Ambulance Service currently operates control rooms in Glasgow, Dundee, Edinburgh, Inverness, Paisley, Motherwell, Aberdeen and Ayr.
Between them, they answer almost 10,000 emergency calls a week.
Three options for change have been identified, which would reduce the number of call centres to three or two.
Unison officer David Forbes said it was unclear whether jobs would be lost and whether there was a system 'which is technically able to deliver the service required. There will still be a need for local co-ordination, certainly of non-emergency services, but perhaps also of emergency services'.
He added: 'I believe that if the option to have three centres is agreed it may ultimately be more expensive to operate than the current system.'
Concerns have also been raised that Aberdeen and other northern areas would lose out in a 'central belt bias' created by any shake-up.