Aer Lingus has warned passengers travelling on long-haul flights to arrive at Dublin Airport a minimum of three hours before their scheduled departure time.

The airline said due to recent “enhanced security measures” by the US Department of Homeland Security, Aer Lingus passengers are “experiencing delays” at US Customs Border Protection at Dublin Airport.

“Aer Lingus guests travelling from Dublin Airport to the US are being advised, via our social channels, aerlingus.com and via SMS, to arrive a minimum of three hours ahead of their scheduled departure to ensure the necessary time needed to complete US pre–clearance before their flight,” a spokeswoman said.

Dublin Airport Authority (DAA) said the airport has been “very busy” for several weeks, with increasing passenger numbers.

“We will be busy this weekend but are not experiencing heavy congestion...and we will have the extra customer care staff in place,” a spokesman for the DAA said.

“We have also hired additional security staff this year to help cope with growing passenger numbers.”

More than 400,000 passengers are expected to travel through Dublin Airport over the Bank Holiday weekend. Passenger figures are up 4 per cent over the same weekend last year, with over 2,669 flights expected to arrive and depart between Friday and Monday.

“This Sunday is set to be the busiest day of the weekend with over 104,000 passengers expected to arrive and depart through both terminals,” the spokesman added.

The DAA recommends passengers arrive 90 minutes before a European flight departs and to add an extra 30 minutes if you’re parking at the airport, while for long haul flights, it recommends three hours.

Separately, Ryanair chief executive Michael O’Leary has criticised new Schengen-area border controls which are causing delays for holidaymakers at some EU airports.

New EU rules introduced following terror attacks require countries to carry out more stringent checks on travellers entering and leaving the Schengen area, which allows passport-free movement across much of the EU.

The change means the details of passengers from non-Schengen countries, such as Ireland, are run through databases to alert authorities if they are known to pose a threat. The new border controls do not apply at Irish airports.

Mr O’Leary said he is “jumping up and down” in frustration at the disruption. On Tuesday just 78 per cent of the Dublin-based carrier’s flights were on time, down from 90 per cent during the month of August as a whole last year.

Passengers at airports in Spain, Portugal, France, Italy and Belgium are being forced to stand in immigration lines for “up to four hours”, according to lobby group Airlines for Europe (A4E).