Passengers arriving into Dublin Airport have had to wait for up to an hour to get through immigration and one senior civil servant warned it was leading to a negative passenger experience.
That is according to documents released to RTÉ News under Freedom of Information.
The longest queues occurred between June and September of last year, affecting people who did not have EU passports in Terminal 2.
Passport control is manned by the Garda National Immigration Bureau.
However, 80 civilian staff are currently being transferred to passport control roles to deal with delays.
The longest queues occurred on 20 July, 31 July, 4 August, 12 August and 8 September.
People with non-EU passports were waiting for around an hour to get through immigration.
The most severe congestion was on the August bank holiday when people arriving in Dublin Airport had to wait for an hour and 20 minutes to clear passport control at one point.
The international standard for clearing passport control is 45 minutes for people travelling from outside the EU.
A spokesperson for the Department of Justice said it was recognised that on occasion queues could spike, but said this affected fewer than 10% of travellers.
She claimed that most travellers are processed in one to ten minutes.
Correspondence released to RTÉ News shows that the Department of Transport and Tourism had been requesting additional personnel from late 2013 on, and warned that staffing levels were not adequate to deal with the August bank holiday.
Lengthy queues were leading to a negative passenger experience, the Department’s assistant secretary John Fearon warned in one letter.
He said the Department spent a lot of time persuading US authorities to adequately staff their pre-clearance operation to ensure there are no delays for people flying to the US.
"It is difficult to continue to negotiate this service when the reciprocal arrangements, including that for inbound US visitors, are open to question," he stated.
In a May 2014 letter to the Department of Public Expenditure and Reform, Mr Fearon called for the situation to be resolved before the peak summer season.
However, the correspondence shows that written agreement was not given to hire the new staff before the August bank holiday weekend.
In an email, William O’Dwyer, an official in the Department of Justice wrote: “Frankly, and to say the least, this is not the position we want to be in as we head into the bank holiday and one of the busiest times at the airport.”
He said the Department of Justice has made it "abundantly clear" to the Department of Public Expenditure and Reform that three-hour queues throughout the airport were a risk.
In September, Minister for Justice Frances Fitzgerald finally announced a programme to use civilian staff for immigration functions undertaken by gardaí, with the addition of 80 staff.
The minister said the process, which would see some functions transfer to the Irish Naturalisation and Immigration Service, was expected to be completed by the end of 2015.
Gardaí will continue to be involved in investigations, arrests and detentions.
There are currently 24 civilians on passport control at Dublin Airport.