France has suggested it could block Romania's entry to the Schengen border-free zone, an area made up of 25 countries where people can travel freely, if Bucharest fails to control the flow of Roma travellers leaving its borders.
In a letter to the European Commission, Francois Fillon, the French prime minister, also said the $5bn sent every year by the European Union as aid to Romania should be used by the Romanian government to keep Roma in the country.
Raising the stakes as Romanian officials arrived in Paris for two days of talks on Wednesday, the French government defended its repatriation of hundreds of Roma in recent weeks and said the Roma emigration from Romania had become a European problem.
"The Romanian government must make this a national priority and if it doesn't, certain things will happen - notably concerning adhesion of Romania to Schengen," Francois Lellouche, the French European affairs minister, said in an interview with Europe 1 Radio.
The EU's top justice official expressed concern over France's expulsion of Roma and said her office was reviewing whether the crackdown complied with EU law.
"I have been following with great attention and some concern the developments over the past days in France as well as the debate sparked in several other [EU] member states," Viviane Reding, the European justice commissioner, said on Wednesday.
"It is clear that those who break the law need to face the consequences. It is equally clear that nobody should face expulsion just for being Roma.
"I have therefore asked my services to fully analyse the situation in France, in particular whether all measures taken fully comply with EU law."
Romania and Bulgaria, where most Roma travellers come from, have been members of the European Union since 2007 and are both due to join the Schengen area next year.
Thousands of Roma people in France are living under the constant threat of eviction after Nicolas Sarkozy, the French president, said in July that he would dismantle 300 of their camps by the end of October.
Six-hundred members of the Roma community have been repatriated from France, mostly to Romania, since the announcement.
Around 10,000 returned to their countries using a "voluntary" procedure last year, which involved the payment of $380 per adult and $125 per child.
Despite growing criticism, Sarkozy's government insists it is acting in accordance with EU law in repatriating Roma who have been in France for over three months without work.
Critics in France, including representatives from right-wing parties, human rights groups and the church, believe the measure is aimed at boosting Sarkozy’s popularity before a general election scheduled for 2012.
The Romanian government has questioned the legality of the expulsions and the European Commission said it plans to issue a report on the legality of the expulsions.