Almost 10 per cent of Irish passport-holders wishing to travel to the US will require a new "machine-readable" passport from October 1st to avail of the US Visa Waiver Programme.
Under the programme, Irish passport-holders can visit the US for 90 days without a visa. However, new regulations require all travellers hold a "machine-readable" passport or else apply for a visa.
All passports issued since 1993 are machine-readable but anyone who received an emergency passport where personal details are hand-written and anyone who picked up their passport at a foreign embassy will need to have a new passport issued.
The new US requirement also means children must have their own "machine-readable" passport or obtain a visa on the parents' passport to travel to the US. An estimated 75,000 children are currently named on their parents' passport.
There are 3.7 million passports in circulation in the Republic, which means almost 370,000 new passports will have to be issued for travel to the US.
A Department of Foreign Affairs spokesman said it could not fully guarantee there would be no delay in processing applications. However, it strongly advised travellers to apply for their passports by post.
An Post's Passport Express Service has experienced some difficulty in recent months.
The spokesman said that in a "large number of cases where there were delays, it was a problem with the forms and how they were filled in".
The delays in June saw a backlog in applications, causing a 50 per cent increase in waiting times.
Normally, applications are processed in 10 working days.
A spokeswoman at the US Embassy in Dublin said machine- readable passports enhance security because they can be scanned on entry and exit points, they provide for rapid identification, and lost or stolen passports are easier to trace.
The fee for a regular 10-year passport is €57. Three-year passports are available to under 18s and over 65s for €12.
There are 27 countries availing of the visa-waiver programme.
From October 26th, 2004, travellers from visa-waiver states visiting the US will also require a passport embedded with a biometric chip. The chip contains personal information such as fingerprints.