Workers are doing unpaid overtime worth billions of pounds each year, a study suggests.
Teachers and managers in particularly are putting in hundreds of hours of overtime free of charge, with 5.3 million people doing £33.6bn of unrewarded work last year.
The TUC is now urging companies to stop relying on staff doing extra hours for free.
They also want them to to make sure their employees take proper lunch breaks, as well as leave on time.
Last year, the 5.3 million employees worked an average of 7.7 hours a week more than they should have.
Chief executives topped a list of those doing the most unpaid overtime, at an average of 13.2 hours a week, followed by teaching staff (12.1 hours), finance managers (11.3 hours) and managers in production and health care (10 hours).
The TUC has warned that working time protections could be weakened when the UK left the EU.
General secretary Frances O'Grady said: "Few of us mind putting in some extra time when it's needed, but if it happens all the time and gets taken for granted, that's a problem.
"So make a stand today, take your full lunch break and go home on time.
"The best bosses understand that a long-hours culture doesn't get good results.
"So we're asking managers to set an example by leaving on time too."
Kevin Courtney, general secretary of the National Union of Teachers, said: "Once again, the TUC has found that teachers and the education sector as a whole are subject to enormous levels of unpaid overtime.
"This situation is untenable.
"Long and unmanageable working hours are the biggest single reason cited by teachers for leaving the profession."