Romanians and Bulgarians have gained the right to work in any of the European Union's 28 countries, prompting politicians to seek to allay fears of an exodus.
The lifting of work restrictions on Wednesday has caused concerns of an "invasion" into Britain and Germany from the EU's poorest countries, but the European Commission says mass emigration is unlikely.
"There are over three million people from Bulgaria and Romania already living in other member states and it is unlikely that there will be any major increase following the ending of the final restrictions," Laszlo Andor, European commissioner for employment, said in a statement on Wednesday.
"In hard times, mobile EU citizens are all too often an easy target."
Britain rushed through measures to ban migrants from claiming unemployment handouts from the moment they arrive in the country and German politicians talking about the threat of social benefits fraud.
Rosen Plevneliev, Bulgaria's president, said in his New Year's Eve speech that the citizens of his country "would like to have a worthy job" at home, and "not to buy a one-way ticket and leave Bulgaria".
Bulgaria and Romania joined the EU in 2007, becoming its poorest members.
Since then, 17 EU countries, including Italy and Sweden, have lifted initial restrictions on their work markets.
Analysts therefore believe that Bulgarians and Romanians who wanted to work elsewhere would have already done so, instead of waiting for Austria, Belgium, Britain, France, Germany, Luxembourg, Malta, the Netherlands and Spain to lift restrictions.