Sixteen Indian citizens, who did not have the right to work in Britain, have been arrested after they were found working in a farm in Evesham in south-west England, official sources in London said.
The group included 12 women and four men. A citizen of Iran was also arrested during the intelligence-led operation by the UK Border Agency.
Officials said steps will now be taken to remove the immigration offenders from Britain.
Officers who carried out the raid on May 28 checked identity documents to establish whether the employees were working legally but found that none of those arrested had any right to work in the UK and some were failed asylum seekers.
The manager of the recruitment agency who supplied the illegal workers was issued with an on-the-spot notice and was warned that he faced a fine of 170,000 pounds.
The arrested Indians had been transported by bus from Birmingham and the Wrst Midlands to plant, pick and prepare salad onions.
Gail Adams, regional director of the UK Border Agency Midlands, told newspersons: "The UK Border Agency is determined to put a stop to illegal working in the Vale of Evesham. We have teams visiting businesses across the county to make sure they are not breaking the law.
"Anyone found to be working illegally should know that we will seek to remove them from the country. Many employers work with us to ensure that they only employ legal workers.
"Our message to employers who do not take this issue seriously is simple - if you employ illegal workers you could be named and shamed, face criminal charges and a hefty fine."