Six people face deportation after being arrested in a raid at Brighton Pier, while a seventh is in police custody.
Police and immigration officials rounded up all the pier staff
Forty police officers and immigration workers entered the pier at 0850 BST on Tuesday and rounded up about 60 staff.
The Home Office has said it was an intelligence-led operation. The pier re-opened at 1220 BST.
Six suspects were taken to a deportation centre near Heathrow Airport with the seventh questioned in Brighton Police's custody centre.
'No terror link'
The six are expected to stay at Colnbrook Immigration Centre before being deported once it has been confirmed whether they were illegal immigrants.
The seventh person, a man, is expected to remain in the custody of Brighton Police.
A spokeswoman said he was being treated differently because his case was more complex than the others, with further investigations needed to establish his circumstances.
She stressed there was no suspicion that his case was linked to the terrorism arrests in the city last month.
Twenty officers from Sussex Police and 20 immigration officers swept onto the pier and gathered up all the staff working there at the time.
The 60 staff were questioned in a fish and chip shop on the pier, which was shut to the public.
The immigration service said most of the people involved co-operated but three people had hidden in the pier's Dr Who exhibition.
The arrested workers are believed to be Brazilian, Colombian, Korean or Malaysian nationals.
Geoff Lockwood, assistant director of the UK Immigration Service, said: "This operation was a direct response to intelligence received that people employed on the pier were in the UK unlawfully.
"Although there is nothing to suggest that there is a particular problem with illegal working in Brighton, today's operation showed that over 10% of pier staff spoken to were in breach of immigration laws.
"The operation was timed and planned to keep disruption to a minimum and those spoken to who were clearly committing no offence were quickly released."
The Noble Organisation, which runs the pier, said it employed around 300 people there and only three of those arrested worked directly for the company.
Director David Biesterfield criticised the operation, saying it "could all have been resolved had the immigration services picked up the phone and asked to look at our records".
"It would have seemed sensible to work with us rather than creating this position of hostility."