Teaching assistants, auxiliary nurses, police community officers and other public services support staff are putting in millions of hours of unpaid overtime, according to new research.
Unison said its study showed the impact of years of job cuts, which had led to "intolerable pressures" across the public sector.
A survey of almost 1,000 workers in the NHS, education, local government, police and other areas found that more than two out of five are doing unpaid overtime most weeks.
Some said they were taking on work of colleagues who had been made redundant, and were working beyond their pay grade.
Four out of five were working harder than a year ago, but a third believed they were much less productive because of cutbacks.
The union said workers felt demoralised as a result of austerity, adding that morale was at "rock bottom".
Unison said cuts had been disproportionately targeted at support staff.
General secretary Dave Prentis (pictured) said: "Support staff such as healthcare assistants and catering workers are among the lowest paid in public services. All too often they're overlooked by politicians, despite the vital jobs they do.
"It's no wonder they feel overworked and undervalued. Many are facing intolerable pressures because of cutbacks, which have triggered staff shortages.
"The Government must commit to funding the jobs needed to guarantee safe, high quality services. A failure to act will undermine standards further and weaken public confidence further still."
Copyright (c) Press Association Ltd. 2018, All Rights Reserved. Picture (c) Anthony Devlin / PA Wire.