Council workers put in seven million days of overtime last year for no extra pay or time off in lieu, according to a survey carried out by public sector union Unison.
The research, based on interviews with 4,000 Unison members in local government, shows that one-third of staff worked unpaid overtime every week for an average of four-and-a-half hours.
Nearly 60% had considered leaving their jobs in the past six months, with 72% of these people saying they felt undervalued by their employers.
Staffing levels have continued to decline, with 20% of members reporting almost daily staff shortages and a 30% increase in the use of temporary staff.
When asked if, in the past 12 months, staff shortages had occurred in their working area or department, eight in 10 members said this was the case, compared to 76% in 2001 and 73% in 2000.
The survey also found that nearly 80% of respondents were very worried about their pensions.
Unison head of local government Heather Wakefield said the survey reflected a workforce that was under pressure, under-valued, under-staffed and under-resourced.
“Each year, our members do more for less and yet face greater insecurity for the future,” she said.
“Pension fears and dissatisfaction with pay are running high, while staff shortages and lack of recognition for the work they do can only add to the serious recruitment and retention problems facing councils.”
Wakefield said Unison was willing to negotiate with the government over pensions, but warned that strike action would be inevitable if there is no agreement.