An Post has said the rise in cost reflects that of other European postal services and a decline in the sending of mail.
In a statement, An post said:
"This domestic price increase, the first in three years (since April 2017), reflects other European postal services’ price increases over the past three years and keeps An Post tariffs in line with the European average.
"Increases in letter prices across Europe reflect the steady decline in traditional letter volumes globally due to e-substitution.
"An Post has invested to ensure that Ireland has one of the best postal systems in the world as it transforms from the old world of traditional letters to the new world of ecommerce parcels.
"Over the past three years, An Post has extended its collection and delivery service across the country six days a week, and evenings; invested in the Dublin Parcel Hub - one of Europe’s most advanced parcel processing centres - which sorted 100 million Christmas parcels during December 2019; Developed a digital platform including Click & Post for 24/7 service and invested in Ireland’s largest electric fleet for 100% emission-free delivery in all our cities by the end of 2020.
"An Post is now working on Phase 2 of its Parcel Investment Plan – a new fully-automated sorting facility for smaller parcels and packages at the Dublin Mails Centre in Clondalkin which will process 70,000 items daily."
Existing stamps will remain fully valid after March 19 but will incur an additional cost.