Nurses in England are being sent ballot papers, asking if they are ready to consider industrial action in their pay dispute with the government.
The move by the Royal College of Nursing (RCN) comes after the government said it would pass on a 2.5% pay rise in two stages, equating to 1.9% over the year.
But nurses elsewhere in the UK will get the full rise in one go.
The RCN says a poll of 2,300 people found 82% see this as unfair and 74% would support nurses taking action.
The RCN promised at its annual conference in April to have the indicative ballot of its members if the government did not reverse its decision.
Unison has also agreed that a ballot of the union’s 450,000 NHS members, including nurses, ambulance crews and paramedics, would be held unless the offer was increased.