Delays of up to a week have forced An Post to bring forward their latest dates for posting with Christmas coming up for e-commerce retailers.
The company's capacity for delivering parcels will be extremely busy due to the rise in demand.
In an email to commercial customers and retailers this week, the company says that this action is necessary "in the interest of fulfilling customers' expectations", RTE reports.
An Post says that delivery by Christmas Day can't be guaranteed for parcels that are posted by retailers after Tuesday, 15th December.
This means that the last dates for posting for people fulfilling online orders was brought forward by almost a week.
An Post says it was "an extremely difficult" choice to do and added they know retailers and online sellers may be dissatisfied by it.
They explained that have had no other option and is making the change so that customers won't be left disapointed.
An post has been a 230% rise in parcel deliveries.
During November, the company have delivered 2.5 million parcels every week.
That number is expected to rise to 3.5 million in the following weeks.
The move will impact on online sales as people weigh up expected delivery times.
An Post explained in statement to RTE that the revised deadline applies only to its "bigger ecommerce retailers and shippers and not to ordinary customers posting parcels and packages for whom the advised latest dates still apply".
Consumers are advised to post Christmas cards to America by Friday 11 December.
Cards to Europe should be posted by 17 December and EU parcels by 17th December.
Cards posted to the UK, the posting date to be sure of delivery of cards and parcels in time for Christmas is 18 December.
The company added: "We prefer to be upfront so that these major online sellers can plan their operations and advise their customers accordingly."
The systems of An Post are running at full capacity and it would deliver three million parcels this week.
