Three men and a woman, all from Belfast, were detained at Belfast International Airport on Monday.
They arrested under the Customs and Excise Management Act after 23,400 suspected illicit cigarettes were seized by HMRC investigators.
The cigarettes, worth an estimated £6,227 in lost duty and taxes, were found after a number of passengers’ luggage was searched.
The four people were released pending reports to the Public Prosecution Service.
Steve Tracey from HMRC, said: “Tobacco fraudsters are costing the UK £2bn a year in lost taxes.
“This is theft and money which should be going to fund public services is ending up in the pockets of crooks.
“HMRC will continue to work in partnership with UK Border Force to challenge this illegal trade.
“Levelling the playing field for legitimate local businesses who cannot compete with their criminal competitors, is at the heart of our strategy to clamp down on the illicit tobacco market.
“We encourage anyone with information about the illegal sale of tobacco to contact our 24 hour hotline on 0800 59 5000.”