The UK Border Agency enforcement teams yesterday arrested as many as 139 suspected immigration offenders across the country as part of a clamp down on people working illegally.
However, the actions have raised fears of racial profiling if the drive was found to be targeting mainly non-whites and ethnic minority communities.
Dave Garratt, the chief executive of charity Refugee Action, warned that the operations could "incite racial tensions".
"Over the last few weeks we've seen some very visible signs of the government's 'hostile environment' crusade.
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Barry Gardiner, an Opposition Labour MP for Brent North in London, has written to Home Secretary Theresa May following reports of spot checks in London, which he said violated "fundamental freedoms".
"We do not yet live in a society where the police or any other officers of the law are entitled to detain people without reasonable justification and demand their papers.
"The actions of your department would however appear to be hastening us in that direction," he wrote.
However, the Home Office has said it makes "no apology" for its actions. "We make no apology for enforcing our immigration laws and our officers carry out hundreds of operations like this every year around London. Where we find people who are in the UK illegally we will seek to remove them," a spokesperson said.
"Immigration enforcement officers conducted an operation... Based on intelligence, where they questioned individuals to check if they had the right to be in the UK," he added.
Immigration Minister Mark Harper said: "Yesterday's operations highlight the routine work we are carrying out every day to stamp out illegal working. We are sending a clear message to employers who choose to use illegal labour - we will find you and you will pay a heavy penalty.
"Illegal working undercuts legitimate businesses and is often linked to exploitative behaviour such as tax evasion and harmful working conditions. We will not allow the growth of a shadow economy for illegal migrants.