Conditions that some migrant workers in the UK are forced to work under could be likened to "a modern form of slave labour", a union boss has warned.
Mr Dromey says many migrants are 'deceived' about work in the UK
Jack Dromey, deputy general secretary of the T&G Union, said it was wrong that migrant workers were often paid less than their British counterparts.
He said some had illegal deductions taken from their pay and were made to "hotbed" in cramped accommodation.
It is "utterly crucial" that migrant workers are treated equally, he said.
Mr Dromey spoke out as he gave evidence to the Lords economic affairs committee, which is examining the impact of immigration on the economy.
The study comes as Home Secretary Jacqui Smith defended a decision not to publicise the fact that 5,000 illegal immigrants were cleared to work in security, amid claims of a cover-up.
She said her priorities were to establish the "full scale" of the problem and take "robust action".
Giving evidence, Mr Dromey said it was wrong to pitch migration against the impact of getting those not in work in Britain into jobs.
"The reality is we're in an expanding economy and an aging population. We need labour. Who is going to do the work, because the economy is expanding and the population ageing," he said.
"To cross continents to seek employment means you are highly motivated. Unfortunately, there are all too many employers taking advantage of the vulnerability of the newly arrived.
"It is utterly crucial that we have equal treatment of migrant workers."
Mr Dromey said that in some areas of food processing there was a problem of a two tier market.
"That does have an impact on wages. It creates a division. It's wrong that two people alongside each other, one is an agency worker, the other directly employed, doing the same work in a food processing company, one gets paid £2 an hour less than the other," he said.
There is "a depressing pattern of workers who are promised the move in their countries of origin, sometimes with such serious deception in terms of what actually happens when they arrive here in Britain that it would in statutory terms of international law be classed as trafficking", he said.
"The awful reality all too often is national minimum wage or less, illegal deductions, deductions for transport, housing, unspecified administrative charges.
"Often workers on national minimum wage having deductions of between £110 and £130 a week, no contracts of employment, compulsory overtime, having to pay for their own safety equipment, and in extreme cases, racial harassment and violence.
"In terms of accommodation, where all too often gangmaster employees or agency employees stay, it is five and ten to a house, sometimes actually sleeping in the premises where they actually work, often illegal evictions.
"I have been into houses ... 16 people in a small house where they couldn't all be there at the same time so it was a hot bedding arrangement."
He told how in a crop picking firm, a pregnant woman had collapsed.
"They were embarrassed about the circumstances in which she had been working," he said.
"When she asked for an ambulance to be called, they said 'by all means, but you realise in this country you have to pay for an ambulance'.
"It's strongly arguable also that in some work places it is discriminatory, in terms of who are those who work on inferior conditions, often overwhelmingly migrant workers.
"A sad reality in modern day Britain is that it is not sufficiently focused on, which at its most extreme, is a modern form of slave labour."