Many people working in the public sector have suffered real terms pay cuts over the last five years, according to the TUC.
The real annual salaries of emergency workers, many of whom will be working over Christmas, have dropped by thousands of pounds, it said.
The Treasury said “difficult decisions” on public sector pay would protect 200,000 jobs.
It added that public sector wages had kept pace with the private sector.
Midwives and firefighters have seen a real terms annual pay cut of more than £3,000 on average, and nurses’ and ambulance drivers’ salaries have dropped by more than £2,000, the TUC said.
Police officers’ pay is down £1,300, it added.
TUC general secretary Frances O’Grady said: “Nearly a million people will be working on Christmas Day this year.
“Ministers should show some seasonal goodwill and end the real-terms pay cuts.
“The government’s Scrooge-like public sector pay cap has to go, to ensure that wages at least keep up with prices.”
But the Treasury said: “The government has made difficult decisions on public sector pay to maintain fiscal discipline and protect public sector jobs.”