Businesses in the UK claimed £32.7 billion worth of free labour from the workforce through employees doing unpaid overtime, according to the Trade Union Congress (TUC).
The TUC's analysis of official statistics suggests more than five million people put in an average of 7.5 hours a week in unpaid overtime during the whole of 2018, equivalent to £6,532 taken out of individual pay packets.
Today (1st March) is the TUC's 15th annual Work Your Proper Hours Day, marking the fact that the average person doing unpaid overtime has effectively worked for free so far this year.
Frances O'Grady, the TUC's general secretary, said: "It's not okay for bosses to steal their workers' time.
"Lots of us are willing to put in a few extra hours when it's needed, but too many employers are taking advantage. Overworking staff hurts productivity, leaves workers stressed and exhausted and eats into time that should be spent with family and friends.
"Bosses who do steal people's time should face consequences. So we're calling for new rights to ensure that employers who break the rules on working time can be brought to employment tribunals."