NHS staff from four of Scotland's unions have announced plans to strike after rejecting a 5% pay offer from the Scottish Government.
The Royal College of Nursing (RCN), Unison, Unite Scotland and GMB members have condemned the offer.
Meanwhile, midwives and maternity support workers have threatened to strike over the pay offer, the Royal College of Midwives has said.
Unite Scotland and the GMB have announced that NHS staff are "prepared to strike".
GMB members rejected the pay offer by 97%.
Unite's membership of NHS staff work in every pay band across the health service and voted to reject the pay offer by 89%. In a consultative ballot, 77% favoured a walkout.
Sharon Graham, the union's general secretary, said Unite's NHS Scotland members rejected the pay offer as it represented a "substantial real terms pay cut" amid an inflation increase of 11.8%.
Scotland's Health Secretary Humza Yousaf said the Scottish Government is disappointed unions have rejected the pay deal and will "look to re-engage with trade unions as soon as we can".
Union bosses have also highlighted the Scottish Government's underspend of £650 million, announced in June.
They say it could be used to fund an improved wage offer for NHS staff.
GMB Scotland organiser Karen Leonard said: "If the minister wants to recruit and retain the people desperately needed to help our NHS recover from the peril it is in, then he must value these key workers better, and particularly those in the lowest pay grades who do not receive the biggest cash increases under this offer.
"However, if these hard truths are not recognised and confronted then industrial action affecting NHS services looks inevitable in the months ahead."
James O'Connell, Unite regional officer, said: "The mandate to move to an industrial action ballot from our NHS Scotland members is emphatic.
"These hard working and courageous workers really deserve far more from the Scottish Government.
"Instead, they are being forced into a position whereby the only way they are going to get a decent pay rise is through strike action.
"This situation is exclusively down to the Scottish Government because they are also hoarding a £650 million underspend."
Matt McLaughlin, Unison Scotland head of health, called on the First Minister to intervene and avoid strikes. He said: "This is the first time since devolution that NHS workers have been balloted for strikes over pay, the First Minister must step in now to ensure that Unison members get a fair deal on pay and that we avoid the need for workplace stoppages as we approach the winter."
Colin Poolman, RCN Scotland's interim director, said: "The Scottish Government must do better to demonstrate they value our nursing workforce and address the years of underinvestment."
Mr Yousaf said: "While we respect the mandate given to trade unions, I am disappointed they have voted to reject the record 5% pay deal for NHS Scotland Agenda for Change staff, and are now holding ballots for industrial action.
"We will consider the next steps and look to re-engage with trade unions as soon as we can, and hope to reach a satisfactory outcome."