Unions are urging the government to tackle "the abuse" of thousands of migrants heading for work in the UK.
The TUC claims that migrant workers are being systematically exploited
They claim that a rise in the number of unlicensed gangmasters has led to a dramatic increase in the exploitation of vulnerable workers.
They say some are forced to put in illegally long hours, are charged for their placements and have to pay employers for their accommodation.
Unison leader Dave Prentis says the situation is "disgusting".
'Rights signed away'
In a debate at the Labour Party's conference in Bournemouth, the UK's largest union Unite is calling for the government to give more rights to agency and migrant workers.
Mr Prentis said it was "despicable" that in the fifth largest economy in the world, migrants were having to make payments to their employers.
He told a fringe meeting ahead of the debate that some migrants arriving at Victoria coach station were having to hand over money on the promise of work.
He said they were told to sign contracts to pay for their accommodation and were forced to sign away their trade union rights.
"We have got workers working all day, then being locked in a caravan in the evening and they can do nothing about it," he said.
Mr Prentis said it was crucial migrant workers knew their rights and especially about the minimum wage.
"We have got to make this issue of vulnerable workers one of the major issues for the coming year," he said.
"We have got to get enforcement so that employers don't abuse their position and we've got to get a government that's committed to it."
Paul Kenny, of the GMB union, warned the government to avoid the "mantra 'British jobs for British workers' because it could play into the hands of racists and bigots".
"I know that's not what is intended, but it is easy to cross the line. Workers are workers," he said.
"Our job in the trade union movement shouldn't be to alienate these people, it should to organise them."