Ambulance staff could be going out on strike across the Midlands over plans to close two of the region's five control centres.
Unison is to hold high-level talks this week to discuss the proposals to shut down the Worcester and Shrewsbury sites.
The reconfiguration proposals will also see the closure of the Stone Lane control centre in Stafford, but a centre handling 999 calls will be opened just two miles away in Tollgate.
Ambulance chiefs yesterday outlined their plans for a new, modern ambulance response structure, which will see the region have two main control centres at the existing West Midlands headquarters, in Brierley Hill, and Stafford. A third site in Leamington Spa will be retained as a support centre.
Officials are expected to rubber stamp the proposals, which will see the number of control staff almost doubled from 62 to 110, days after the regional West Midlands Service merges with Staffordshire Ambulance Service on October 1.
Unions reacted furiously yesterday to the potential loss of two rural centres.
Ray Salmon, West Midlands regional organiser for Unison, said valuable local knowledge would be lost under the proposals.
He said: "Potentially this could result in a ballot for action. We will be discussing this week what course of action we will take.
"We are not very happy about the way this has happened. Historically we have had a good working relationship with management where we all get together around a table to discuss proposals before they become public. But this has not happened this time.
"If there was any action we would go region-wide, because that is what the law says we have to do.
"The issues would have to be very serious for us to consider this - but these are."
Ambulance chief Anthony Marsh said the proposals were not set in stone and he would listen to other ideas during the three-month consultation process, which was launched yesterday.
But he said the current structure was not "fit for purpose" and doing nothing was not an option.
He said: "We have put forward proposals which we believe could improve the performance of the West Midlands region.
"If someone genuinely has a better idea, the consultation is an opportunity to share it with us so that we can consider it in the round. It does not give me any pleasure to sit here and say we are proposing the closure of two emergency control centres but I genuinely believe it is the right thing to do.
"That is why we have been so open and explicit so that we can do whatever we can to accommodate staff."
Mr Marsh said there would be no redundancies under the plans and staff would have have opportunities to change jobs and secure promotion through the restructuring.
The sale of the three sites would bring in £2.9 million which would fund expansion work in the regional hubs.
The trust would also save about £500,000 a year under the plans, but Mr Marsh said the proposals were not motivated by financial concerns.
Unison representative Tracey Jones, speaking at yesterday's meeting for staff working at the Shrewsbury control room, said: "Since the possibility of losing the Shropshire control became public knowledge, the people of the county are rallying to support any move that could allow the control room to remain open."