Labour MEPs have been accused of selling out the country's economic interests by voting to amend the UK's opt-out of the Working Time Directive (WTD) against British government policy.
The Labour MEPs have aligned themselves with the French socialists in the European Parliament in pushing for the end to the working time opt-out. They are supporting a move to close a loophole in the EU's 1993 Working Time Directive that allows firms to negotiate individual opt-outs in employee contracts.
This would strip employees of their right to work more than 48 hours a week and give trade unions and mandatory staff councils a veto on whether individuals can choose to exceed the 48-hour limit.
Another amendment would further prohibit all workers spending more than 65 hours week on the job in any week.
Since this limit would include time spent on call, such a move would cause havoc in vital services such as the NHS.
The vote comes as the French government plans to relax its laws enforcing a 35-hour working week in a bid to halt the country's mounting unemployment crisis.
In Britain, employers' groups reacted to the MEP's move with fury.
The Forum of Private Business (FPB) said it was "appalled" by the "hard faced obduracy" of Labour MEPs, accusing them of selling British business interests "down the drain" by voting with the socialist group in European Parliament on 20 April.
"Labour MEPs should hang their heads in shame if they vote to scrap the UK's opt-out of the WTD," said the FPB's Chief Executive Nick Goulding.
"They are flying in the face of sensible and reasoned Government policy. A deletion or amendment of the opt-out would critically harm the flexibility of Britain's labour market, crippling smaller firms.
"To remain competitive and provide jobs, products and services, Britain's opt-out must not be removed. In the real world, it is necessary for employees to put in long working weeks for peak periods of demand, large orders or deadlines. This is not draconian or unreasonable, but pragmatic and practical."
Last September, the foreign office said: "It is not for the EU to tell people how long they can work, and this is exactly the wrong the way to run an economy."
Research by the Institute of Directors (IoD) has also reinforced the importance of the opt-out, finding that over four out of 10 UK firms make use of the provision.
The IoD said the wholesale abolition of the opt-out would consequently do significant damage to British business.
In an open letter to UK politicians, Miles Templeman, Director General of the IoD, said: "The Government's consistent support for the opt-out has been widely appreciated across the business community. The difficulty is that some British MEPs have taken a very different approach, voting against the Government's line and in favour of scrapping the opt-out."
Loss of the British opt-out would particularly hurt key industrial sectors, the IoD survey revealed. Of businesses in the construction, mining and transport fields an overwhelming 85 per cent said the loss of the opt-out would make management more difficult.
The ban would also cause major problems in financial services and tourism, the IoD said.
Miles Templeman, said: "With the European Parliament's Employment and Industry Committees both due to vote on the issue during their meetings on 19-20th April, I would urge all British MEPs to vote in favour of retaining the opt-out. IoD members would be deeply disappointed if British MEPs were to fail to uphold our national economic interests on labour market flexibility."
The IoD, said it was equally concerned with proposed changes to the EU Services Directive, also up for discussion in Brussels this week.
A new report suggesting major amendments would undermine the most important aspects of the draft Directive, the IoD said. Of particular concern are proposals to drop the Country of Origin Principle. This would leave companies wishing to test the market or trade temporarily in other Member States subject to the regulations of the country of destination.