The Queen has been asked to intervene in a dispute over the pay of NHS staff who have to work during the Diamond Jubilee celebrations in June.
Unite said many NHS employers in England were treating June 5 as a normal day, even though the Government has declared it a bank holiday.
In a letter to the Queen, Unite's head of health Rachael Maskell said: "I am asking if you could make an intervention to ensure that hard-working NHS staff in England will be afforded the opportunity, with the rest of the nation, to celebrate Your Majesty's Diamond Jubilee."
Unite said NHS staff who work on June 5 should receive the same nationally-agreed public holiday pay rates as other public sector workers.
"Employers across the UK are refusing to pay staff, who have to work within the service on this public holiday, the normal enhanced rates due for public holiday working," said Ms Maskell.
Commenting on her letter, she added: "NHS employers have raised mean-spiritedness to an art form - but they still have time to reverse their decision.
"It is highly ironic that the Government has declared a public holiday to celebrate the Queen's 60 years on the throne, yet many NHS employers intend to blatantly flout the spirit of this once-in-a lifetime day that working people would like to enjoy."