The online school books retailer schoolbooks.ie has guaranteed that all delayed orders will be delivered by Friday.
The company has said that a technical issue at the company's warehouse had caused a backlog of 5,000 orders.
An extra 30 staff have been hired to fill the delayed orders at the warehouse in west Dublin.
The company has already filled 50,000 orders for schoolbooks, copies and other back to school essentials since June.
Schoolbooks.ie has been in operation for nine years.
It has said that this is the first time it has had such problems.
The company has apologised to parents for the anguish caused at what can already be a quite stressful time of year.