The ballot will run until 26 September and will determine whether the union's 100,000 NHS members will strike this autumn. The union claims 1.3 million health workers in the UK have seen their pay fall by 15% in real terms since the coalition came to power in 2010.
The pay deal in April of this year saw England's 600,000 NHS staff receive a 1% pay increase, with health secretary Jeremy Hunt ignoring the recommendation of the Pay Review Body to offer a living wage increase to lower-paid workers.
The Welsh Assembly agreed to pay all NHS staff in the country the living wage, along with a one-off £160 payment. However, there is still disagreement on the terms of the deal, so Welsh NHS workers will be included in the ballot.
A similar arrangement was agreed in Scotland, with low-paid staff receiving an extra £300 per year to take their salary up to living wage. As a result there will be no industrial action there.
Unite head of health Rachael Maskell accused Hunt of treating NHS workers "with contempt" in the dispute over pay.
"Our members have an opportunity from today to vote in favour of industrial action and send a stark message that the health secretary should sit down with the unions and listen to our proposals for fair pay for the biggest workforce in the UK," she said.
She also stressed that any industrial action would take into consideration "concern for patient care".