UK Border Agency said it stopped two vehicles on the A52 at Somerby Hill near Grantham at 06:00 BST.
Officers said the men, 11 Indian nationals and the other a Pakistani, were among 24 men and were probably set to work on a farm in the county.
The 12 men have been taken to immigration detention centres pending their removal from the UK.
Rachel Challis, from the UK Border Agency’s Lincolnshire local immigration team, said: “Businesses that take on illegal workers should also be warned that they face heavy fines and possible prosecution.
“Any foreign national who is in the UK illegally should be in no doubt that they will be found, arrested and removed from the country.”








