The Revenue Commissioners has confirmed that hundreds of customers were sent letters stating they owed more tax than is the case.
Around 350 customers have contacted the Commissioners to say they had received letters that put their tax liabilities higher than they should be.
The Commissioners have accepted there were errors in up to 1,000 letters sent out last week, but said the mistakes have been recognised and there will be no financial implications for any customers.
They said they are contacting all affected customers to point out the errors.
A spokeswoman for the Commissioners said they send out around 100,000 items of post each week and the letters containing errors represent about 1% of all the post sent out last week.
A small number of people contacted RTÉ News in recent days to say they had received letters stating they owed sums that were large multiples of their expected tax liability.