The new president of the European Commission has warned the UK not to “beat up” EU migrants as it tries to cut immigration.
Jean-Claude Juncker said people from Poland, Romania and Bulgaria were “earning their wages” and should not be treated as criminals.
Prime Minister David Cameron wants to change Britain’s relationship with the EU ahead of an in/out referendum.
Last month he urged EU support for curbs on welfare payments to migrants.
The UK government has admitted the scale of EU migration means it is likely to miss its target of cutting net migration to the tens of thousands before the general election in 2015.
Mr Cameron had previously vowed to “get what Britain needs” and change the free movement of people, but this met strong resistance from his European counterparts who see it as a fundamental principle of the EU.
During a debate on Austrian TV, Mr Juncker, who came to office at the start of November, said he wanted Britain to remain an active member of the EU.
But he went on to suggest that the knock-on effects of curbing free movement could have a negative impact on the City of London.