Britain will announce on Tuesday plans to restrict the influx of migrant workers from Bulgaria and Romania.
The move marks a shift from the open-door policy Britain has adopted to eastern European workers since the European Union's enlargement and follows concerns the country could be inundated with unskilled workers who undercut locals.
The government plans to make a statement about "transitional controls" on Bulgarian and Romanian workers at 1030 GMT on Tuesday, a spokesman at the Home Office (Interior Ministry) said.
The Home Office is expected to say Britain will take a limited number of unskilled workers from Bulgaria and Romania to do jobs such as fruit-picking but would not offer immediately a general right to work, newspapers reported at the weekend.
Bulgaria and Romania join the bloc in January, giving their citizens a right to free movement within the EU.
Home Office minister Baroness Scotland told parliament's upper house on Monday the government was planning transitional controls for Bulgaria and Romania.
"The approach to labour market access for the new member states will be gradual ... We hope to be able to put forward a scheme which will both be welcoming but also take advantage of some of the things that we have learned from the accession of the other eight," she said.
Britain was one of three EU members, along with Sweden and Ireland, that gave unfettered access to workers from eight other eastern European countries that joined the bloc in 2004.
The government said in August that more than 400,000 workers from the eight countries had come to Britain, far higher than official forecasts that between 5,000 and 13,000 new immigrants would arrive each year.
That prompted calls from the opposition Conservative Party and some members of the ruling Labour Party for Prime Minister Tony Blair to restrict immigration from Bulgaria and Romania.
"There are concerns about our labour market but we all want to be clear that anything that is proposed is workable and effective," Foreign Secretary Margaret Beckett told a news conference on Monday.
Critics of labour market controls argue they will encourage more immigrants to work illegally since Bulgarians and Romanians will have the freedom to live in Britain from January.