A row over France's crackdown on Roma (Gypsy) migrants from Romania and Bulgaria looks set to dominate a summit of EU leaders in Brussels.
President Nicolas Sarkozy was furious after an EU official compared France's removal of Roma with the deportation of gypsies during World War II.
EU justice commissioner Viviane Reding also threatened legal action against France.
The EU leaders will also discuss ways to prevent a new financial crisis.
And they will seek to co-ordinate their approach towards emerging powers like China and India.
'Heat of the moment'
This was not meant to be a summit about the Roma, but Mr Sarkozy seems determined to go on the offensive in Brussels to defend France's reputation as the home of human rights.
He is said to be scandalised by Ms Reding's criticism, mockingly suggesting the Roma should go to her country, Luxembourg.
With tension rising to an unprecedented level, European Commission President Jose Manuel Barroso distanced himself from Ms Reding's comparison with World War II deportations.
"One or other of the expressions used in the heat of the moment may have given rise to misunderstandings," Mr Barroso said.
"Vice-President Reding did not want to establish any parallelism between what happened in the Second World War and the present."
Mr Barroso called for more dialogue.
Romania and Bulgaria will want their say, and so will Italy and other nations that have expelled Roma less publicly than France.
Right and irreproachable
What seems to have angered France most is Ms Reding's apparent comparison between the persecution of Jews and gypsies in Nazi-occupied France, and the current wave of expulsions of the Roma.
"This is a situation I had thought Europe would not have to witness again after the Second World War," she said.
France's Europe Minister Pierre Lellouche responded that a plane ticket back to Romania or Bulgaria is not the same thing as death trains and gas chambers.
Mr Sarkozy meanwhile insists his policy is right and irreproachable.