Union leaders have raised fears that "penny-pinching" bosses will refuse to give workers time off to celebrate the Queen's Diamond Jubilee.
The TUC said it was concerned that some firms might treat Tuesday June 5 as a normal day even though it has been designated as a bank holiday, giving workers the chance of a four-day break.
A significant number of employers forced staff to work or take annual leave on the Royal Wedding day last year, causing "needless ill will", said the TUC.
General Secretary Brendan Barber said: "Everyone is looking forward to the Diamond Jubilee weekend. There will be parties and celebrations taking place up and down the country. It's also half-term so many families will be planning to go away.
"The long weekend will give millions of workers a chance to recharge their batteries and spend much needed time with friends and family. The economic benefits of bank holidays may be hard to be measure, but they are priceless.
"Sadly hundreds of thousands of staff are likely to miss out on the festivities because some tight-fisted employers are refusing to recognise the Queen's Jubilee and intend to treat the Tuesday as a normal working day.
"The many shop workers and emergency services staff who have to work during the bank holiday weekend should not be forgotten either. Extra paid leave and contracted overtime pay is the very least they deserve."