Immigration enforcement officers raided the Edgware branch of Sami's restaurant on Sunday, arresting two men said to be working illegally.
The men - a 37-year-old Indian national and a 33-year-old Pakistani national - were temporarily released and ordered to report to Immigration Enforcement while their cases are progressed.
Staff were questioned to establish whether they had the right to live and work in the UK.
The business was served a notice warning that financial penalties of up to £20,000 per illegal worker arrested would be imposed unless it could demonstrate that appropriate document checks were carried out, such as seeing a passport or Home Office document confirming permission to work.
David Seymour-Smith, head of the north London Immigration Enforcement team, said: "Illegal working is not victimless and can involve the exploitation of some of society's most vulnerable people. It also defrauds the Treasury of vital funds, undercuts businesses that provide an honest trade and cheats legitimate job-seekers out of employment opportunities."
According to a message on the restaurant's phone, it is closed for refurbishment. Staff at other Sami's branches said the owner was on holiday and that no one was available for comment.