The TUC will use its annual conference in Brighton next month to push for a 48 hour working week in line with the European Working Time Directive (WTD).
Union leaders say Britain must abandon a 'work 'til you drop' culture and are calling on the Government to scrap the opt-out from the WTD.
Currently, employees can choose to work more than 48 hours a week if they opt out of the directive, and business leaders want this to continue.
CBI director general Digby Jones told BBC Online: "People should have a right to say no to long hours, and the directive rightly gives them that protection.
"But they don't want unions and politicians telling them when they can work or for how long. That would be over-zealous interference of the ‘nanny state'.
“Further restrictions on working time would be a kick in the teeth for many firms, particularly smaller ones."