Immigration officers have raided two Derbyshire restaurants and arrested four men.
The raids took place at Maazi restaurant in Causeway Lane, Matlock, and Maazi restaurant in Main Road, Hathersage, at about 6pm on Friday.
Staff were questioned to check if they had the right to live and work in the UK.
At the Matlock restaurant, officers arrested two men – a 34-year-old Nepalese man and a 25-year-old Pakistani man.
At the Hathersage restaurant, officers arrested two Pakistani men – a 28-year-old and a 33-year-old.
A Home Office spokesman said: “All those arrested had overstayed their student visas.
“The 33-year-old man was detained while steps are taken to remove him from the UK.
“The other men were ordered to report regularly to the Home Office while their cases are progressed.
“Both businesses were warned that they will be liable for a financial penalty of up to £20,000 per illegal worker found, unless evidence is provided that the correct pre-employment checks were carried out, such as seeing a passport or a Home Office document.
“This is a potential total of £40,000 for each business.”
Alison Spowage, assistant director for immigration enforcement in the East Midlands, said: “Our teams carry out regular operations such as this to tackle illegal working.
“Employers who use illegal labour are defrauding the taxpayer, undercutting genuine employers and denying work to legitimate job seekers.
“There are simple checks employers should carry out to ensure their staff have the right to work in the UK. Those who choose to ignore the rules will face heavy financial penalties.
“I would urge members of the public with detailed information about suspected immigration abuse to get in touch.”
The immigration enforcement officers were acting on intelligence.
Information to help employers carry out checks to prevent illegal working can be found HERE.
Anyone with information about suspected immigration abuse can call Crimestoppers on 0800 555 111.