A government campaign will warn bosses that they face large fines and prison sentences if they are caught employing illegal migrant workers.
The Home Office will run radio and print adverts ahead of a tightening of the law on illegal labour in February.
Employers could be fined up to £10,000 for every illegal worker they negligently hire, or could face up to two years in prison.
The immigration minister said firms would have no excuse to break the law.
Liam Byrne said: "Illegal working attracts illegal migrants and undercuts British wages. That's why we're determined to shut it down.
"The message is clear for employers - we will not tolerate illegal working."
Well, I certainly don't disagree with that, and I hope that the advertising campaign, and the new laws, succeed in deterring employers from employing illegal immigrants. But I do wonder whether the government in general, and the Home Office in particular, are not being a tad hypocritical. After all, not only has their repeated failure to tackle illegal immigration probably done more to "attract illegal migrants" than anything any private company - however avaricious - could do, but they have themselves been caught employing illegal immigrants!