The TUC says UK workers put in the longest hours in Europe
Britain has moved a step closer to being forced to limit the working week to 48 hours for all employees.
Euro MPs have voted in favour of ending Britain's opt-out from the EU working time directive.
Britain is determined to keep the opt-out and will now start talks with EU ministers in an effort to keep it.
The UK does not have a veto on the issue but it is expected to join forces with other countries who back its position in order to get its way.
A decision is expected early next year following "conciliation" talks with the European council of ministers.
If Britain is forced to axe its opt-out, the law will come into force in three years' time.
Gary Titley, leader of Labour's MEPs, who voted to keep the opt-out, said the two sides were so far apart on the issue that the talks would probably end in stalemate and the opt-out would continue.
"Continuing with the status quo is the most likely outcome," Mr Titley told BBC News, adding that unlike many of his Labour colleagues he believed maximum working hours should be set at a national level.
But Mats Persson, of pressure group Open Europe, which campaigns to keep the opt-out, said there was a chance Britain would be overruled, as it had been in the past on the issue of junior doctors' hours.
MEPs voted in favour of scrapping the opt-out by 421 votes to 273, with the majority of Labour MEPs voting to axe it, in defiance of Prime Minister Gordon Brown.
Shadow business secretary Alan Duncan said: "On the day when unemployment rose above 1.8 million, Gordon Brown's MEPs have voted resoundingly against the opt-out that helps to protect British jobs.
"Reducing the flexibility of our labour market going into what even government ministers are calling the deepest recession we have ever faced, is an economic madness that only the Labour Party would be capable of."
Thousands of trade union members marched on the European Parliament to urge an end to the opt-out, ahead of Wednesday's vote.
And leaders of the UK's biggest union, Unite, urged British MEPs to "stop the UK's long hours culture".
But on Monday business minister Pat McFadden told the BBC it would be a mistake to end the opt-out during an economic downturn when people might need to work extra hours.
HAVE YOUR SAY
They couldn't have picked a worse time to try to stop people working when they need to. How about letting the person decide how long they want to work?
The exemption from the working time directive was negotiated by the Conservative government in 1993 and is used to some extent by other member states, for members of the medical profession for example, although the UK is the only country which has opted out of it altogether.
Conservative and Liberal Democrat MEPs say the opt-out should continue but Plaid Cymru MEP Jill Evans and the Green Party's two British MEPs are also against it.
Open Europe estimated ending it in 2011 - as some MEPs want - would cost the UK economy between £47.4bn and £66.45bn by 2020.
CBI deputy director general John Cridland said European Parliament amendments which would stop people being able to choose to work more than 48 hours would "replace opportunity with obstruction".
"If your partner has lost their job, should Brussels stop you from putting in extra overtime to support your family?," he said.
But the unions argue it is a health and safety issue.
Unite joint general secretary Tony Woodley said: "Tired, overstretched workers are not productive workers and are putting themselves and others at risk, such as in the transport industry where we know, for instance, that tired drivers are more dangerous than drunk drivers."