The union represents the majority of ambulance staff working for the NHS in Scotland.
The GMB union has voted to reject an improved NHS pay deal from the Scottish government.
The union represents NHS ambulance staff, nurses, porters and radiographers
It said 66% of their members voted to reject the improved offer, which would have seen workers receive average 7.5% pay uplift.
The GMB suspended a planned 26-hour ambulance strike last month and put the new offer to members in a vote.
Members of Unite and Unison voted to accept the offer earlier this week.
Ballots of the Chartered Society of Physiotherapy (CSP) and Royal College of Nursing (RCN) members are ongoing.
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