As raids on illegal workers are launched at hundreds of businesses across the country, campaigners are using leaked government documents to warn those being targeted.
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Video: Fatima Manji reports, and Home Affairs Select Committee Chair Keith Vaz tells Jon Snow that the operation centurion appears not to be based on intelligence, but documents refer to "particular nationalities and industries".
The Anti-Raids Network, which obtained the documents, says the government is pusuing a political agenda and has tipped off workers.
The two-week crackdown is aimed at workplaces - including care homes, hotels and restaurants, construction sites, recruitment agencies and small businesses - that could be employing illegal immigrants.
"It is a clear attempt to demonise migrant labour and satisfy the right-wing political agenda on immigration and the EU," said one campaigner.
The raids, known as Operation Centurion, are being carried out by government officials at firms believed to be employing illegal immigrants.
On Tuesday morning, men waiting to be picked up in Ilford, Essex, for cash-in-hand work on construction sites were arrested as part of the operation.
A Home Office document seen by Channel 4 News highlights nationalities in specific industries who are being targeted, with one entry describing Nigerians working illegally in barber shops.
Another talks about laundries employing Eritrean nationals, who are described as "not the best nationalities for us, but a new sector nonetheless".
There are phone stalls which "appear to have foreign nationals working on them, some of which don't speak fantastic English", and there are "nail bars with a Vietnamese connection".
A Home Office spokesman told Channel 4 News: "I should like to be very clear that the Home Office does not engage in racial profiling and any suggestion to this effect is both abhorrent and completely without foundation.
"Our enforcement activity, conducted in conjunction with other government agencies, is intelligence-led and targets sectors of the economy where illegal working is suspected. We do not perform 'fishing expeditions' and in the case of the current operation we have worked carefully with employers who share the public's concerns about illegal working."
It is believed the operation will also focus on health and safety issues where vulnerable and migrant workers are known, or suspected, to be employed.
Areas to be looked into include payment of the minimum wage, and where accommodation is provided by the employer and is grossly overcrowded, subject to change at short notice, or not subject to a formal tenancy agreement.
Staff paid cash in hand or working excessively long hours will also be included.