Delegates at the union's annual healthcare conference in Brighton this week unanimously rejected the government's offer of a staged 2.5 per cent pay award, and to support industrial action if the deal is not improved.
Unison senior national officer Mike Jackson told delegates: 'We do not take this lightly. In the health service we don't take industrial action unless in the most extreme circumstances.
'If the government is going to introduce Tory policies we will respond to them in the same way we responded to the Tories.'
Another Unison representative called for members to launch 'a summer of discontent', taking measures such as refusing to answer phones in a bid to 'disrupt senior managers' targets'.
Delegates voted for a 'significant percentage pay increase above the rate of inflation', and rejected an amendment to put a specific figure to their demands.
Unless the government agrees to the demand 'within a reasonable period', with payment backdated to 1 April, Unison will ballot its 450,000 healthcare worker members and recommend a vote for industrial action up to and including a strike.
The phased pay award, announced in March, was intended to keep wages within the government's 2 per cent inflation target.
The Society of Radiographers, the Royal College of Nursing and general union GMB have also voted in favour of industrial action.
Unison head of healthcare Karen Jennings said: 'The government ignores this growing wave of anger at its peril. We will unite with other health unions who have rejected the offer and with public sector unions fighting for a fairer pay deal.'
But a Department of Health spokesman defended its position: 'The award represents a sensible increase, fair for staff, affordable for the NHS, consistent with the government's inflation target as well as protecting jobs and services.'
NHS workers in Scotland were given the full pay rise from 1 April, in what some see as a political move before the May local elections.