An employee in the collector general's office double-debited tax from the bank accounts of 1,100 companies and organisations last week.
He or she deducted an extra €71 million but hardly anyone noticed.
The mistake led to each entity losing on average €65,000, but the Revenue received very few complaints, according to a spokesman. "Most were not aware of it until we brought it to their notice."
The employee, who has a role in the direct debiting of taxes due from the taxpayers' bank accounts, is understood to have activated the debits on Tuesday of last week and then again the following day. He or she immediately realised the error and drew attention to it.
A spokesman for the Revenue said it was currently returning the money to the parties affected, and would have the process completed by Monday.
He said the deductions mainly involved PAYE and PRSI, but also some VAT and income tax.
Each entity affected is to be contacted by the Revenue and told what has happened. The Revenue will refund any charges or fees incurred as a direct result of the excessive withdrawal of funds. It will also apologise to the parties.
The Revenue spokesman said it did not believe the error had happened before. Although a large part of the direct-debiting process was automated, there was human involvement in activating it.
A spokesman for the Irish Taxation Institute said he had no knowledge of any such error occurring before.
"It's unfortunate but, thankfully, it is rare. The system generally is very effective and credit is due to the Revenue for that. And they have moved quickly to correct what occurred."
