Employers that impose a blanket ban on watching football during the World Cup risk demotivating staff and losing hours through unauthorised sick days, the TUC warned today.
The union body called on employers to allow staff the opportunity to watch games during working hours and let them claim back the time afterwards.
Although England only has one game scheduled to start during the day - the final group match against Slovenia, which kicks off at 3pm on 23 June - the TUC is also urging organisations to consider the one in five UK employees who work outside core hours, and those of different nationalities who might want to watch their home team.
The union, which has issued advice for staff wanting to watch the tournament, believes the World Cup is the perfect opportunity for employers to embrace flexible working.
TUC general secretary Brendan Barber said: "People in England work the longest hours in Europe, and we believe rigid working hours contribute to their unhappiness. Whether it's about watching great sporting events like the World Cup or collecting children from school, allowing people more flexibility makes them happier and, ultimately, more productive for their employers."
Fahim Rahman, an associate at law firm Allen & Overy, called on employers to view the World Cup as a great opportunity to boost morale in the workplace.
"Allowing games to be televised at work or letting people watch some of the action at their desks will ensure a positive and celebratory approach to business as usual in the office. With only one England game being played during working hours absenteeism shouldn't be an issue, although employers should remember that not all staff will only be interested in England games."
However, alcohol charity Drinkaware has warned that the number of people going to work with a hangover will increase in June and July, having a direct impact on workplace productivity up and down the country.
Chris Sorek, chief executive of Drinkaware, said: "An international sporting event like the World Cup will inevitably capture the attention of the nation and is a great time for people to come together, but hangovers at work are likely to increase. That's why we have teamed up with Bupa to provide employers with handy tips on staff drinking and hangovers at work, to make the event a better experience for everyone."