Over 450,000 taxpayers are over-paying Revenue and are urged to claim that money back.
Figures from the tax collection agency show each of these people are about €660 worse off.
Close to a million PAYE employees have handed over €620 million too much to Revenue in the past three years.
Speaking to Newstalk, personal finance editor with the Irish Independent, Charlie Weston, says there are a number of reasons people might be overpaying.
"It is because they are probably not on the right tax rate, they could be not claiming what they are entitled to either.
"There a tax reliefs and credits that they may not have correct. You might be entitled to the home carers credit, or you have got married recently and are entitled to be taxed at a lower rate."
"Revenue is encouraging people to engage with them, and they are writing to 50,000 people at the moment."
He said they are asking people to go to MyAccount.ie on the Revenue website and look at a preliminary end of year statement which would indicate if you have overpaid tax or not.
Mr Weston is encouraging people to claim what they are entitled to if they have overpaid.