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The TUC said one in four people have been forced to sign an opt-out document, which allows them to work more than 48 hours a week.
Time's Up For Long Hours, a how-to guide to opting back in, includes a letter people can send to their employers to inform them they no longer want to work more than 48 hours a week.
Sending this letter is all an employee needs to do and it is illegal for an employer to take action or sack an employee because they have made this choice.
The TUC said many employees do not know their rights. Only one in three know there is a 48-hour limit on the working week.
TUC general secretary Brendan Barber said, "The UK's long-hours culture is a threat to the health and safety of employees and a threat to the growth of the UK economy. Employees are tired and stressed and business is unproductive.
"The EC should end the opt-out to the EU Working Time Directive when is reviewed later this year.
"Unions feared that employers would abuse the opt-out and this is what has happened. The TUC will continue to ensure employees are informed of their right to a reasonable working week."
The guide Time's Up For Long Hours is available at