Friday is the final day before the £20 paper note is withdrawn from circulation.
The Association of Commercial Banknote Issuers (ACBI) announced the change several weeks ago.
The paper notes have been replaced by polymer notes which are more secure and harder to counterfeit. They are also more environmentally friendly.
Polymer notes from Bank of Ireland, Danske Bank and Ulster Bank have been circulating since 2019.
A spokesperson from ACBI said: "Thanks to the work that Bank of Ireland, Danske Bank, and Ulster Bank have already undertaken to swap the older paper notes with the more secure, environmentally friendly polymer notes."
Issuing banks will continue to accept all Northern Ireland notes from their own customers.
What should you do with your £20 notes?
The ACBI suggests that customers should:
Deposit them into a bank account
Exchange them for polymer notes
And for non customers Bank of Ireland, Danske Bank and Ulster Bank have agreed to exchange the £20 paper note up to the value of £250 provided photographic ID is presented.
Other banks, building societies and The Post Office may continue to accept and exchange Northern Ireland paper notes after 30 September.
Retailers may refuse to accept Northern Ireland paper £20 banknotes from the 30 September 2022 at their own discretion.
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