David Cameron faces an awkward confrontation with his Polish counterpart tomorrow after complaining about immigrants from the country abusing the benefits system.
Donald Tusk is to demand that the Prime Minister explain his comments when the two leaders speak on the telephone.
He has also reportedly warned that Poland will block any change to EU rules that could give immigrants less access to welfare than UK nationals.
The escalation in tensions came after Mr Cameron hit out at British-based migrants claiming benefits for children living in their home country.
"I don't think that is right and that is something I want to change," he told the BBC over the weekend. "It's a situation that I inherited.
"I think you can change it, I think it will take time because we either have to change it by getting agreement with other European countries, and there are European countries who, like me, think it's wrong that someone from Poland who comes here and works hard - and I'm absolutely all in favour of that - but I don't think we should be paying child benefit to their family back at home."
Mr Cameron said one way of changing that was "the treaty change that I'll be putting in place before the referendum that we'll hold on Britain's membership of the EU by the end of 2017".
But Mr Tusk told a press conference today that it was unacceptable to single out a nationality as abusing the system.
"We will not agree to it if these are changes that would stigmatise any particular national minority," he reportedly said.
"Nobody has the right to single out Poles as a particular group that abuses or exploits something."
Downing Street defended Mr Cameron's remarks, saying it was "perfectly fair" for him to give an example.
"This issue around child benefit, it is an important one. The Prime Minister was absolutely right to raise it and he will continue to do so," the premier's spokesman said.
"The changes we are making would apply more widely but I think it is perfectly fair for the Prime Minister to give an example."
The immigration row in Britain has continued to rage, with Ukip leader Nigel Farage saying the numbers arriving should fall even if it harmed the economy.
The Ukip leader told the BBC Radio 4 Today programme: "If you said to me 'Would you want to see over the next 10 years a further five million people come into Britain and if that happened we would all be slightly richer?', I would say 'Actually, do you know what? I would rather we weren't slightly richer and I would rather we had communities that felt more united and I would rather have a situation where young unemployed British people had a realistic chance of getting a job'."
Mr Farage said there should be no "open door" for migrants from new EU entrants Bulgaria and Romania, and called for a five-year halt to all immigration by people wishing to settle permanently in the UK.
London Mayor Boris Johnson said Mr Cameron was "completely right" to stop migrants claiming benefits for the first three months after they arrive in the UK.
The Tory mayor told radio station LBC 97.3: "We don't want to be slamming up the drawbridge being completely horrible to people.
"If you want to come and work here you can do that but there should be a period before which you can claim all benefits and it seems entirely reasonable to me that they should extend that to two years.
"I think he is right about this business about child benefit. Why should British taxpayers be paying the child benefit of people who may be working in Britain but whose children are living in Poland?"
Mr Johnson said people must be "realistic" about the way Britain acts as a "magnet" for people in countries where benefits are less generous.