The Home Office has launched a last-minute campaign in Bulgaria and Romania to discourage workers travelling to Britain without a work permit when the countries join the EU on Monday.
The £280,000 advertising strategy comes amid concerns that the accession of the two nations will lead to a surge of migrant workers like that from Poland and other eastern European nations after the last enlargement.
The Government has introduced labour market restrictions in a bid to prevent a repeat and has been using television, radio and hoardings to get the message across in Romania and Bulgaria.
Some 8,000 posters have been put up and 40,000 leaflets distributed across the two countries.
The Mail On Sunday newspaper reported that one hoarding in the Romanian capital, Bucharest, warns: "Don't come to Britain without a work permit."
In Bulgaria, a television advert shows a worker turning up at Sofia airport for a flight to Britain. He cancels his plans, however, after reading a sign stating: "Even after January 1 you will need a permit to work in the UK."
The campaign is being run by the International Organisation for Migration (IOM), but funded by a Home Office grant. It was launched on December 14 and will last until March 30.
A Home Office spokesman said: "It is in everyone's interest to ensure that people from Bulgaria and Romania clearly understand the rules we are putting in place."
Meanwhile, the Sunday Telegraph newspaper claimed that fake qualifications are being sold in eastern Europe to help would-be migrants obtain work permits.
The paper said it had obtained counterfeit documents for jobs including nurses, engineers and lorry drivers.
