Four people have been arrested on suspicion of being in the UK illegally in Lincolnshire.
Two men and two women were taken into custody and a restaurant owner given a penalty warning after raids on two Chinese food outlets in Grantham.
Visits were carried out by police and officials from the UK Border Agency, which has its own Lincolnshire team.
Immigration officer James Leebetter said Wednesday's night's raids should act as a warning to others.
He said: "We do get out and we do disrupt as much illegal working as we can.
"We have limited resources but we do generally have success with our visits in this area."