Ambulance crews in the West Midlands and Shropshire are to start industrial action next week in a dispute over pay and conditions.
Unions representing the service voted for action last year in a dispute over a new pay deal for NHS workers.
The strikes will take place between 0700 and 0900 GMT on 9, 16 and 23 February. Staff will start work-to-rule action from Tuesday.
The NHS trust said talks were taking place and it had contingency plans.
Talks will be held between the unions and the trust on Thursday.
The Professional Ambulance Personnel union (Apap) has warned that if no progress was made its members would start a series of strikes, starting with two-hour walkouts at selected ambulance stations, at the end of next week.
Apap does not represent volunteer, private ambulance crews or non-emergency ambulance service personnel.
General secretary Mark Weatherhead said that under the deal, called Agenda For Change, some of his members were facing a pay cut of £3,500.
Unions say they had originally agreed a higher pay scale for paramedics and technicians.
'Hopeful of a deal'
"The processes which were agreed through negotiation have been completely disregarded," he said.
"Apap has exhausted all avenues to resolve this dispute through negotiation and has made the decision to go for industrial action with a heavy heart."
Apap had set a deadline of 1600 GMT on Monday to reach an agreement with the Department of Health and the West Midlands and Shropshire Ambulance Service NHS Trust, but it passed without any progress being made.
Previously, chief executive of the trust, Barry Johns, said the issue of ambulance pay banding was not confined to the West Midlands.
"It is now a national concern. Therefore we have limited room for manoeuvre."
Unison, which represents most ambulance workers in the West Midlands, said it was hopeful of reaching a deal.