The migrants are believed to have spent 13 hours in a fridge prior to being airlifted to hospital. They were later arrested by UK Border Force.
The distress call has been sent from the ferry off Start Point at 7:30 p.m. on Sunday, after the men were found hiding in the car ferry Epsilon, operated by Irish Ferries.
However, the migrants were very lucky and have already made full recovery, according to police.
To avoid migrants arriving in the United Kingdom, ferry companies are fined by the UK for each stowaway coming to Britain and must also pay for the flights back.
The number of immigrants caught in 2017 trying to board a ferry to the United Kingdom in Bilbao is 1,251 - 3 times the number for the whole of last year.