By Daniel Hunter
Data released by the Office for National Statistics (ONS) show that the number of Romanians and Bulgarians working in the UK rose by a quarter in the last three months.
The data shows that 141,000 were employed from April to June compared with 112,000 in the previous three months, up nearly 26%.
Temporary restrictions on the type of jobs people from the two countries can do are due to expire later this year.
This has led immigration campaigners to claim that there will be an even bigger increase next year.
Migration Watch UK, which campaigns for tighter controls on immigration, said the latest figures were in line with its estimate that net migration from Romania and Bulgaria would stand at about 50,000 a year for the next five years.
"We hadn't expected this early uptake - quite a considerable increase - nine months before our labour market is open and I think it does suggest that there's a good deal of interest in these countries in coming to work here," Migration Watch chairman Andrew Green told BBC Radio 4's Today Programme.
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