A human-trafficking operation netted €18m from hundreds of desperate immigrants by funnelling them through Dublin Airport with the help of Aer Lingus staff.
The smuggling scheme was exposed after a major sting operation on a flight from Madrid, involving the Special Detective Unit (SDU) and officers from the Garda National Immigration Bureau.
Further arrests are now expected in the human-trafficking operation which is understood to have enormous international links, including the Italian Mafia and Chinese Triads.
Two Aer Lingus employees, aged 56 and 61, have already been arrested on the suspicion of assisting the people-smuggling operation.
A 28-year-old Chinese national, who entered the country illegally, was also arrested.
Three men are due to appear in Dublin District Court this morning.
Gardaí investigating the unprecedented people-smuggling operation are expected to make more arrests in the near future.
The Irish Independent has learned that the smuggling operation came to light after a man who entered Ireland illegally attempted to leave on a flight to another EU country. Authorities noticed that there was no official record of the man ever entering the country, and an investigation began.
Sources have stated that each person pays at least €10,000 to the smugglers, but the amount could be up to €30,000. About 600 people have been smuggled into Ireland by the organised crime gang in the past number of years, meaning they would have netted in the region of €18m.
"The massive operation includes criminal gangs from Italy and Eastern Europe as well as China, and the majority of illegal immigrants smuggled into Ireland would be Chinese nationals," a source said.
Gardaí are examining whether the flights involved in the criminal network originate from other EU cities, including Rome and Madrid.
A senior garda said that there was always a fear of airline staff assisting such criminal enterprises.
Assistant Garda Commissioner John O'Driscoll, who is in charge of Special Crime Operations, added that Ireland could suffer reputational damage if successful Garda operations such as this one did not take place.
"There is always the danger that employees - and this is worldwide - who have the capacity to facilitate illegal immigration will do certain acts that may assist in that regard," he said.
"The one thing for sure is that Ireland's reputation would be greatly damaged if we didn't show a capacity to continuously monitor our immigration control and detection of breaches where they took place.
"The figures I have given in terms of the ongoing refusal of leave to land and ongoing monitoring over many years and recognition of potential corrupt practices involved is what will be highlighted and acknowledged at an international level," Mr O'Driscoll added.
Both Aer Lingus and the Dublin Airport Authority said they were co-operating with the ongoing Garda investigations but would not comment any further.
Fresh measures are expected to be introduced this year, including the Advanced Passenger Information (API) system.
It requires people travelling to a particular country to submit their passport details and information about themselves before they travel to the country.
This is expected to be implemented by March.
Gardaí are satisfied there was no terrorist or human-trafficking link to the international smuggling operation they smashed at Dublin Airport over the weekend. But they are very concerned that Dublin is being targeted by a global crime network as a potential back-door route for illegal immigrants into the UK.