The Famous Turkish Kebab in Enniskillen could be fined up to £10,000 for employing an illegal worker.
Acting on intelligence UK Border Agency officers visited the takeaway in Darling Street on Friday and arrested a 24-year-old Turkish man after checks showed he was in the country illegally.
The man is now in immigration detention in Larne in County Antrim while steps are taken to remove him from the UK.
Janet Wiseman of the UK Border Agency, said: "Foreign nationals who are in this country illegally should be in no doubt that they will be found, arrested and removed from the UK.
"Companies that think they can undercut competitors by employing illegal workers should be warned that they will face heavy fines and possible prosecution," she added.
"We are sending a simple, clear message to people who are in the country illegally - more raids are planned and you will be caught," said Wiseman.
The Famous Turkish Kebab now faces a fine of up to £10,000 for employing the illegal worker.
To avoid the penalty, the employer must prove that legally-required checks such as taking copies of a passport or a Home Office document were made on the worker before he was given the job.