More than a million people in the UK are set to be working this Christmas Day.
The TUC estimated that 1,104,000 employees will work on Wednesday, an increase of 22,000 since 2016.
And many service sector workers will not get extra compensation for working on December 25, said the TUC.
Retailers such as Homebase, Home Bargains and Aldi are closing for Boxing Day and the TUC is urging other shops to follow suit.
Paddy Lillis, general secretary of the shopworkers' union Usdaw, said: "The trend for more stores to open longer over the festive period inevitably has a big impact on shopworkers' Christmas Day celebrations.
"Finishing late on Christmas Eve and then getting straight back to work on Boxing Day means that Christmas Day is not a proper break.
"We welcome those retailers not opening on Boxing Day and we urge others to follow their example."
Care workers and nurses account for the biggest share of those on duty, totalling more than 300,000, said the union organisation.
A large army of chefs (39,000), kitchen assistants (29,000), waiting staff (18,000) and bar staff (15,000) will be working in hotels, pubs and restaurants, while 14,000 police officers and 18,000 security guards will be at work, it was indicated.
Christmas Day services will also see 25,000 members of the clergy kept busy.
General secretary Frances O'Grady said: "We owe a huge debt to all those working on Christmas Day. As we spend time with our loved ones, they keep Britain ticking over.
"Many on duty on will be on low pay, especially in sectors like hospitality and social care. They deserve to be fairly rewarded for the essential services they provide.
"People working in shops during the manic festive period should be given time off with their families."
