The possibility of an amnesty for illegal workers in Britain should be debated, a key union figure has said.
Mr Dromey says the question is what to do about illegal workers
Jack Dromey, Deputy General Secretary of the TGWU trade union, estimated there could be 500,000 people working in the UK without permission.
Mr Dromey said these immigrants "lived in fear" of being found and were exploited by their employers.
He also said that it would not be possible to deport this number of people from Britain.
The issue of illegal workers has troubled the government this week after it emerged that five such individuals arrived to work as cleaners at the Home Office.
Initially, it emerged that the men were stopped when they first turned up for work due to "alertness" of staff.
But now the Home Office is investigating new allegations that they had cleaned immigration service offices for years.
Meanwhile, Mr Dromey said: "Yes it is true that there are probably half a million here without documents. The question is what we do about that?
"They live in fear of a knock on the door and they are exploited by too many employers."
He added: "What we need therefore is a sensible approach which does not criminalise those good men and women. You can't deport half a million workers.
"Who would clean? Who would cook? Who would pick in our fields? The time has come for a debate around an amnesty for those workers."
'Out of control'
But Liberal Democrat President Simon Hughes said there was a "difficulty with an amnesty".
"The problem is that just makes it easier in the future for people to come here thinking that they can get the right to stay here later," he told BBC News 24.
"It means that all those who have been sent home will have a complaint as it were that they were treated unfairly. It means that there will be two sorts of treatment."
He added that recent allegations over illegal immigrants working as cleaners in the Home Office showed the department had "not got its own act together literally inside its own territory".
"No home secretary in recent times has been able to manage the immigration service, the police, the prison service and all the other home office functions - it is too big and, I am sad to say, it is absolutely out of control," he said.