Revenue is writing to 130,000 PAYE taxpayers who have paid tax but have not claimed any additional tax credits or reliefs in the last five years.
It is reminding them that there is a four-year time limit for claiming a refund of tax.
Revenue has issued letters over the last few years to assist taxpayers in claiming their due entitlements and ensuring they only pay the correct amount of tax.
Analysis of a previous campaign suggests that the letters have a significant positive effect on taxpayer engagement with Revenue.
Pat Murphy, National PAYE Manager in Revenue's Personal Division, has timely advice for taxpayers.
"You can claim a refund of tax paid if there are entitlements you are due but have yet to claim," he said.
"However, there is a four-year time limit for claiming tax refunds and the deadline for 2015 claims is December 31, 2019, so now is a good time to check that you have claimed all of your entitlements."
For taxpayers who want to make a claim, the quickest, easiest and most convenient way to do so is online using PAYE Services, which is available in Revenue’s myAccount portal.
The services in myAccount are accessible on all mobile devices.
Mr Murphy said: "Even if you did not get a letter from Revenue, you can review and update your tax record online at any time, using PAYE Services in myAccount.
"When you submit a claim, it is processed and verified by Revenue and most online refund claims are paid within five working days.
"So, there is still plenty of time to submit your claim and have your refund paid into your bank account before Christmas."
- There is a four-year time limit for claiming tax refunds, so if you have a claim for 2015 you will need to submit it by December 31, 2019.
- The quickest, easiest and most convenient way to submit your claim for tax back is online using PAYE Services in myAccount, which is accessible on all mobile devices.
- If you are not already registered for myAccount, you can register quickly and easily on the Revenue website at revenue.ie.
- If you add your bank account details to your myAccount profile, any refund due can be paid directly into your bank account, usually within five working days.
Below are just some of the areas in which you may be entitled to claim a tax refund.
You can claim relief on the cost of health expenses.
These can be your own health expenses or those of any individual, as long as you paid for them.
You generally receive tax relief for health expenses at the standard 20% rate of tax.
Nursing home expenses are given at the highest rate of tax, which is up to 40%.
You can claim relief for non-routine dental care. This includes crowns, veneers and tip replacing.
You cannot claim relief for routine dental care, such as fillings, tooth extraction and scaling or cleaning.
Tuition fees paid for third level education
You can claim tax relief on fees, including the student contribution, that you have paid for third level education courses.
This fee may be paid by a student, or on behalf of a student.
No relief is available for examination fees, registration fees or administration fees.
Flat rate expenses
PAYE customers can claim for flat-rate expenses.
These cover the cost of equipment an employee needs for work.
This equipment may include tools, uniforms and stationery.
The costs must be directly related to the nature of their employment and they must incur these costs in performing the duties of their employment.
Flat-rate expenses are available to a wide range of professions.
You can find details on the flat-rate expenses list here.