Managers in the hospitality and catering sector do nine hours and 36 minutes of unpaid overtime on average each week, according to the TUC.
This means that if they worked all their unpaid overtime at the start of the year, their first pay day would be 10 March.
The TUC also calculated that the additional work would net them nearly £5,000 extra over 12 months.
TUC general secretary Brendan Barber said: "Most catering and hospitality staff are hourly paid, and so will at least be paid when they do long hours, but managers in the sector are usually expected to put in extra hours for nothing."
Overall the industry was placed fifth in the TUC's unpaid overtime league table, which was produced as part of the union's Work Your Proper Hours Day, which is today.
The union is urging workers to start on time today, to go home on time and to take their proper lunch break.
Working the most unpaid hours are teachers and lecturers, which do 11 hours and 36 minutes unpaid overtime a week.
By Chris Druce
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