Users of the Passport Express service are currently experiencing an average delay of five days in having their applications processed.
The Passport Office has apologised for the delay, which it says is partly due to increased demand on services, following the most recent naturalisation ceremony for 3,000 foreign nationals.
The Department of Foreign Affairs, which oversees the Passport Office, says express applications are currently taking 15 days to process, instead of ten.
It says temporary staff are being used to clear the backlog.
More than 90% of passport applications are made through the express service, which is jointly run by An Post and the Passport Office.