It singled out the conditions of Portuguese workers on the Home Office headquarters site in Westminster, London, where Bouygues is the main contractor. Bouygues has denied claims that it has treated anybody unfairly.
UCATT has been refused permission to go on the site. UCATT general secretary George Brumwell is seeking urgent talks with home secretary David Blunkett over the issue.
The DTI, along with the Foreign and Commonweath Office, Citizens' Advice Bureau, the TUC and Portuguese authorities, have sponsored the publication, which gives advice on employment rights.
Employment relations minister Gerry Sutcliffe said some Portuguese nationals had been misled into thinking they would be considered illegal workers here. He said: "We are taking a 'know before you go' approach, distributing this information in Portugal and the UK."
He said the leaflet includes advice on agreeing an appropriate contract before leaving Portugal and information on the minimum wage.
Citizens' Advice Bureau director Teresa Perchard said that she had seen a big increase in the number of European Union nationals, particularly from Portugal.
She said: "We welcome the DTI's initiative to provide Portuguese workers with information about their employment rights, which are the same as those for UK nationals."