RYANAIR passengers travelling tomorrow evening and on Saturday morning are being urged to check-in early and print off their boarding passes - or they could be hit with a charge of up to €45.
The budget airline is shutting down its website for 10 hours for a vital upgrade to help it process the 1.2 million visitors it has each day.
It will be down from 7pm tomorrow until 5am on Saturday 20 - and during that time travellers will not be able to check-in online or make new bookings.
Ryanair spokesman Robin Kiely said charges would still apply to passengers if they did not check in early.
"The standard costs of €45 if you don't check in, or €15 if you misplace your boarding pass will still apply," he said.
"We have contacted all of our passengers travelling in the time period to let them know the site will be down - this is on top of the regular mailing sequence that we supply to passengers urging them to check in and print their boarding passes.
"If we decided to waive the check-in fee on this occasion we could have 250,000 passengers queuing up at check-in desks all over the place, which would cause problems for everyone.
"But we find that 99.5pc of our passengers check in electronically with no problem, so we don't anticipate any difficulty for this situation," he added.
New bookings or changes to flights will not be possible during this web closure.
"We sincerely apologise for any inconvenience caused by this upgrade, which will further improve Ryanair.com, Europe's largest travel website," said Mr Kiely.
He said that passengers would not notice any difference in its website once it was relaunched after the upgrade.
"We fly 1,600 flights a day between 6am and midnight, and we have 1.2m unique visitors to our site every day, so it is vital that we have an efficient and easy to navigate site," said Mr Kiely.
"We are hoping to launch a new website in the autumn as we aim to constantly improve upon it," he added.
Mr Kiely said the web upgrade tomorrow and on Saturday would affect all passengers travelling globally and not just those in and out of Ireland.