A series of strikes is expected to test the new Tory government's resolve over the next few weeks.
The Royal College of Nurses, which has never gone on strike before, is considering industrial action if the government tries to cut salaries to fund its flagship election promise of a "truly seven-day NHS".
Elsewhere, Network Rail staff are due to walk out for 24 hours from 5pm next Monday – a bank holiday – in a dispute over pay, job security and working conditions.
Union officials warned that the first UK-wide rail strike for two decades would bring services to a "standstill" on 26 May.
The National Union of Teachers passed a motion at its conference in April calling for a ballot on industrial action if the government did not increase funding for schools.
North Sea oil workers are also expected to be balloted about the first strike in the offshore industry in a generation.
The Unite and GMB unions are negotiating with employers about changes to working conditions, but Unite has reportedly told its members to be "ballot ready".
Staff members at the National Gallery in London are planning strikes on Wednesday and from 26 May to 4 June amid a dispute over privatisation and a union official's dismissal.
BBC radio studio managers have also backed industrial action over a row about time off in lieu.
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