EU Justice Commissioner Viviane Reding has urged the European Commission to take legal action against France over its deportations of Roma (Gypsies).
Ms Reding called French actions a "disgrace". She deplored the fact that a leaked official memo contradicted assurances given to her by France.
France voiced "astonishment" in response to her statement on Tuesday.
It deported nearly 230 Roma on Tuesday alone, flying them to Romania from Paris and Marseille.
Nearly 160 were flown out of the French capital to Bucharest, and 69 out of Marseille, AFP news agency reports.
All had agreed to be repatriated in exchange for cash payments of about 330 euros ($423, £274) per adult and 100 euros per child.
More than 1,000 people have been deported to Romania and Bulgaria since late July, when President Nicolas Sarkozy linked illegal Roma camps to crimes such as prostitution and child exploitation.
Critics see the law-and-order crackdown as a way for Mr Sarkozy to boost his flagging popularity amid discontent over government cutbacks.
The BBC's Oana Lungescu in Brussels says Ms Reding's rebuke amounted to incredibly strong language from a European commissioner about a big member state.
EU disciplinary action against France could lead to substantial fines.
France denies that the expulsions target an ethnic group, saying they are done on a case-by-case basis. It also insists that most of them are voluntary.
Last week Euro MPs accused the Commission of failing to protect the Roma deported from France.
Speaking at a news conference on Tuesday, Ms Reding said she would propose legal proceedings by the Commission over France's treatment of the Roma and that a Commission decision would be taken within two weeks.
The case would then go before the European Court of Justice in Luxembourg, she said.
France is accused of violating EU law, which bans discrimination against any ethnic group or nationality.
"I am personally convinced that the Commission will have no choice but to initiate infringement proceedings against France," Ms Reding said.
"The role of the Commission as guardian of the treaties is made extremely difficult if we can no longer have confidence in the assurances given by two ministers in a formal meeting," she said.
"This is not a minor offence in a situation of this importance. After 11 years of experience in the Commission, I even go further: this is a disgrace," she said.
Recently French Immigration Minister Eric Besson and Minister for Europe Pierre Lellouche briefed Ms Reding on France's handling of the Roma issue.
On Monday the French press published a leaked French official memo suggesting the Roma had been specifically targeted by the authorities.
The memo contradicted assurances to EU officials from Mr Besson and Mr Lellouche that immigrants were being treated on a case-by-case basis.
The order, dated 5 August, was sent from the interior ministry to regional police chiefs.
"Three hundred camps or illegal settlements must be cleared within three months, Roma camps are a priority," it said.
Mr Besson told France 2 television on Monday that he was "not aware of this circular".
Last week the European Parliament urged the French government to halt the deportations - a call rejected by Paris.
On Monday Mr Lellouche told the BBC he was "sick and tired" of the criticism directed at France over the Roma.
French Foreign Ministry spokesman Bernard Valero called Ms Reding's statement unhelpful on Tuesday.
"We don't think that with this type of statement, that we can improve the situation of the Roma, who are at the heart of our concerns and our action," he said.