New figures show the number of EU migrants registered to work in Yorkshire and Humberside has plummeted from 19,000 in 2006 to a projected 9,000 this year.
The exodus has been largely blamed on the recession, with thousands of jobs axed in construction, social care, agriculture and hospitality industries, plus the falling value of the pound, leading many, particularly those with families to support, to return home.
But in spite of 230,000 people being unemployed in Yorkshire, evidence has emerged of employers targeting the remaining migrants for new jobs.
Fears have been raised that this will add to the perception of foreigners taking the jobs of British workers. But, ironically, concerns have also been raised by firms. If the exodus continues some businesses may not be able to fill the posts migrants have left because British-born workers will not take them.
Last week the Government's equality watchdog announced it was writing to Cleckheaton-based sliced meat manufacturer Forza AW over allegations of discrimination against British job seekers after the firm advertised for workers who "must speak Polish".
The company says the advertisement was a mistake. Elsewhere it is claimed firms across the region have engineered shift patterns to make jobs only attractive to migrant workers, who often travel to the country without their families and are prepared to work longer, more unsocial hours.
Helena Danielczuk, an outreach worker for the Federation of
Poles in Yorkshire and the Humber and who works with migrants in Bradford, said: "We know
of food manufacturing companies across Yorkshire who
have changed their shift patterns to accommodate migrant workers.
"They want to make efficiencies and these workers are much more profitable and easier to exploit.
TUC regional secretary for Yorkshire and the
Humber Bill Adams said: "Any practices to exclude people applying for jobs is against the law and is definitely going to whip up tension.
"But it is the unscrupulous employers who are deserving of the blame,not hard-working migrants. It makes me ashamed, some of these employers are getting away with murder."
Tens of thousands of workers poured into the region after 2004 when the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Slovakia and Slovenia joined the EU. In particular, huge numbers of Polish migrants settled across Yorkshire – in 2007 a total of 10,000 were thought to be living or employed in North Yorkshire alone.
Tensions between foreign and domestic workforces in other EU countries have led to violent clashes and unions in Britain have reported a rise in the number of complaints about racist abuse of migrant members following the economic downturn.
Regional manager for Yorkshire and Humber Migration Partnership Rob Warm, who has documented the dramatic fall in the numbers, said: "When jobs are scarce the relationship becomes more tense.
"The state of the economy makes people more anxious about their own opportunities and it could become more difficult for migrants."
Conservative MP John Greenway, chair of the Council of Europe's migration committee and whose Ryedale constituency contains a greater percentage of migrants than any other in Yorkshire, said: "For the immigrants that are staying here there needs to be a greater effort of integration into communities – we have to get a strong grip on this."
The warnings come as the centre-left Institute for Public Policy Research (IPPR) think tank said a fixed cap on immigration could be a political own goal.
Tory leader David Cameron has pledged to set a cap on net immigration but said the level should be decided each year according to economic need.
Net immigration should be in the "tens of thousands rather than hundreds of thousands".
But, in a new report, the IPPR warned that a cap of 40,000, as proposed by the Cross-Party Group on Balanced Migration, would mean "drastic changes" and would threaten both economic performance and the rights of British nationals and settled migrants to be with their families.