The Prime Minister is being urged to take action in 2017 to stop the pay of public sector workers "plummeting".
The GMB union launched a campaign to persuade ministers to halt the "squeeze" on public sector wages, which it says has hit the living standards of workers in the NHS, education, local government and other services.
Nurses have lost more than £14,600 since 2010 because salaries have not kept pace with inflation, care assistants have lost almost £10,000, teaching assistants £8,800, social workers £12,900 and refuse collectors £9,000, the union said.
Unions have been telling the Government that workers are suffering because of its 1% pay cap in the public sector, which is set to continue for years.
GMB national officer Rehana Azam said: "Public servants perform an absolutely vital role in our society - we would be utterly lost without them.
"The fact that their wages are dramatically falling in real terms demonstrates a lack of respect for hard-working frontline workers who do decent work and deserve to be honoured with decent pay.
"Theresa May needs to make the most important New Year's resolution of her life - to make sure vital public servants are properly paid for the important work they do."