The head of the country's biggest business group told union activists that industry continued to oppose moves to give new rights to temporary and agency workers.
Richard Lambert, director-general of the CBI, said his organisation did not support the European Union Agency Workers Directive, due to be discussed by employment ministers today.
Unions have been pressing for the Directive to be adopted in this country to give agency and temporary staff the same rights as full-time workers.
But Mr Lambert told the TUC Congress in Brighton that the CBI opposed the Directive in its present form.
"We don't believe it would protect vulnerable workers - in fact, we think it could make it harder for some workers with family and other responsibilities to find their way into permanent jobs.
Recent CBI research shows that large numbers of agency temp placements would simply disappear."
But Mr Lambert said he agreed that vulnerable workers should be protected from exploitation.
"Responsible employers recognise the importance of the national minimum wage and accept that employment tribunals provide an essential recourse for those denied their basic rights.
"They acknowledge the many ways in which employment rights have been strengthened over the last 10 years. "There should be no hiding place for those who operate outside the law - they should get clobbered."
Mr Lambert said rigorous enforcement of existing rules was the right way forward.
He told delegates that the UK had more flexible labour markets than most other European countries and much better social protection than in the United States.
"This, I am convinced, is one of the main reasons why we in the UK look more favourably on free trade than citizens in other big economies."
Mr Lambert said there was a lot of work to do to improve the skills of British workers and said the record of this country did not compare as well as its international competitors.
Up to 30,000 temporary agency jobs in the West Midlands would be put at risk if the Government does not reject attempts to resurrect agency workers legislation, according to new figures from the 2007 CBI/Pertemps employment trends survey.
Fifty-five per cent of firms in the West Midlands said they would 'significantly' reduce their use of temporary agency workers if the UK adopts the proposed Directive.
The survey found that currently four per cent of the workforce in the West Midlands are temporary staff.
These are said to form a small but economically important section of the workforce and offer vital flexibility to businesses at times of a surge in demand. The CBI calculates nearly 30,000 of these would be put at direct risk by the Directive.
Nationally, 252,000 jobs would be jeopardised.
Susan Anderson, the CBI's director of HR policy, said: "Many thousands of West Midlands firms rely on the flexibility temporary staff provide during times of high demand for their products and services.
"The jobs generated are also a source of convenient, quality employment for thousands of people in the West Midlands.
"The Government must stand firm against the drive to revive this damaging Directive."
Celia Perry, director at recruitment specialists Pertemps, said: "People choose to take up temporary work for a number of reasons, sometimes to gain experience with a view to securing a permanent role or to build work around their other commitments.
"The proposed EU law would threaten a key source of flexibility for the region's businesses."