"No one in the NHS (National Health Service) takes strike action lightly - today shows just how desperate they are," GMB National Secretary Rachel Harrison said.
"This is as much about unsafe staffing levels and patient safety as it is about pay."
The union said they will now meet with representatives in the coming days to discuss potential strike dates before Christmas.
Britain's health service is braced for a wave of unprecedented industrial action this winter, with the ambulance announcement following scheduled strikes by up to 100,000 nurses on Dec. 15 and 20.
(Reporting by Farouq Suleiman; editing by William James)