A record 5.26 million people worked unpaid overtime last year, clocking up an average of more than seven hours a week without pay, according to a new study.
The TUC said workers were missing out on almost £5,500 a year by working so much unpaid overtime, worth around £29 billion to the UK economy.
One in five employees regularly put in extra hours for no extra pay last year, with public sector workers most likely to work unpaid overtime, said the TUC.
The number of workers doing unpaid overtime was the highest since records began in 1992, the research found, with 5.26 million people clocking up an average of seven hours 12 minutes unpaid overtime every week.
The TUC dubbed today Work Your Proper Hours Day - the day the average person doing unpaid overtime would start to get paid if they did all their unpaid work at the start of the year.
TUC General Secretary Brendan Barber said: "With tough economic conditions making employers reluctant to recruit, existing staff are picking up much of the increasing work load through unpaid hours.
"While most staff are happy to put in some extra free time to help their company through, forcing staff to endlessly put in too many hours could lead to increased stress levels, which can make staff ill and reduce the quality of the work they do.
"Public sector workers - already experiencing a sharp cut in their earnings as they have their pay frozen and pension contributions raised - will be understandably upset about the amount of extra unpaid work they are expected to do with the threat of redundancy looming over them.
"Work Your Proper Hours Day is a light-hearted campaign and today is an opportunity for bosses to thank staff for going that extra mile.
"But there is a serious side to excessive overtime, irrespective of whether staff get paid for it. Bosses should always be on the lookout for a damaging long hours culture in their workplace and take steps to protect their workforce."
Workers in London were most likely to work unpaid overtime at eight hours a week, followed by those in the East Midlands (7.5 hours) and North East and Scotland (both 7.4 hours), said the TUC.
The report warned unpaid overtime was likely to increase in the public sector because of heavy job losses expected in the coming months as a result of Government spending cuts.Reuse content