The European Parliament have voted to scrap Britain's opt-out from the maximum 48-hour working week.
A 421-273 vote of MEPs was hailed as a "triumph" as MEPs cheered the result - but months of negotiations with EU governments and the European Commission now follow.
Most British Labour MEPs backed the call to end the opt-out - clashing with Prime Minister Gordon Brown, who wants it to stay.
At least 14 other EU countries now take advantage of an opt-out, once championed only by Britain as vital to business flexibility.
With an economic downturn in full swing, more countries want the option of exceeding the 48-hour week - and earlier this week the Commission admitted it had reversed its own opposition to keeping the opt-out because of pressure from so many member states.
But on Wednesday MEPs bucked the trend, voting by a bigger margin than expected in favour of a resolution that the opt-out should be gone by 2011.
It would force employers across Europe to stick to a maximum 48-hour week, averaged over a year.
The arrangement to average the maximum out provides sufficient short-term scope for bosses and workers to work longer hours if necessary, supporters of the ban argued.
But opponents said it should not be up to the EU to determine the working patterns of very different employment cultures in the member states.
Tory MEP Philip Bushill-Matthews said after the vote: "Socialist MEPs have won the battle, but they must not be allowed to win the war. The British Government must dig in and defend the opt-out. Fifteen EU nations now take advantage of the flexibility provided by the opt-out and none of them should back down."
