Business groups have reacted angrily to reports the European Parliament is again considering abolishing the UK's opt out of working time rules.
A report calling for the removal of the right for certain employers - including those in the UK - to ask staff to work more than the maximum 48-hour week is to form the basis of the revised Working Time Directive.
A draft of the paper by Spanish socialist MEP Alejandro Cercas, leaked to the Financial Times, claimed the opt-out poses a "serious risk to workers' health and safety".
He called for it to be phased out by 2010 as well as introducing greater flexibility by lengthening the period used to calculate average weekly hours from four to 12 months.
While trade unions maintain that working excessive hours is damaging the health of UK workers, business groups claim attempts to limit the opt-out threatens the competitiveness and productivity of firms.
David Frost, director general of the British Chambers of Commerce, said: "This could be bad news for British businesses. The flexibility of our labour market is a great strength of the UK economy.
"Losing the opt-out will erode the UK's competitive edge and fly in the face of EU objectives to boost growth and improve competitiveness. The UK government, MEPs and businesses must fight together to ensure this damaging proposal to scrap the working hours opt-out is rejected."