The TUC’s analysis of official figures shows that more than 470,000 workers in the region did almost eight hours a week unpaid overtime in 2015.
That is worth, on average, £5,792 each.
Work Your Proper Hours Day is the day when the average person who does unpaid overtime would start to get paid if they did all their unpaid overtime at the start of the year.
To mark it, the TUC is calling on staff to take a proper lunch break and leave work on time. Managers are also being encouraged to lead by example and encourage their staff to work their proper hours.
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Public sector workers contributed £10.8 billion of unpaid overtime last year. Public sector employees make up a quarter of total employees but produce a third of all unpaid overtime.
The most unpaid overtime is done by teachers and education professionals, followed by financial institution managers, production managers, functional managers such as financial, marketing, personnel managers, and managers in health and care services.
People aged 40 to 44 are most likely to do unpaid overtime, with more than one in four in this age group putting in unpaid hours compared to an average of one in five for all UK workers.
TUC Regional Secretary Lynn Collins said: “Too many workplaces in the North West tolerate a long-hours culture.
“That is why we are calling on employees to take a stand today on Work Your Proper Hours Day and take a full lunch break and go home on time.”