Drivers from Northern Ireland will have to carry an insurance green card while driving across the border to the Republic of Ireland from January.
The new rule will apply after the end of the Brexit transition period.
The Irish Department of Transport has confirmed the requirement to BBC News NI.
"A green card is a document issued by your insurer that proves you have motor insurance cover when driving in another jurisdiction," a spokesperson said.
The spokesperson added "As it stands, following the transition period, a green card will be required for vehicles from the UK, including Northern Ireland, being driven in Ireland or other EU Member States, unless the European Commission declares otherwise."
The department further clarified that it is not an offence under Irish or EU law for GB or Northern Ireland-registered vehicles to drive in Ireland without a GB sticker attached to the vehicle.
In July, the UK government released guidance on driving in Europe, saying that an International Driving Permit (IDP) may be required in some countries from 1 January 2021.
However, the department spokesperson said there will be no requirement for holders of a UK driving licence to hold an IDP when visiting Ireland after the end of the transition period.
The Association of British Insurers confirmed that Irish drivers crossing the border into Northern Ireland will not require a green card, but that "as things currently stand" NI drivers travelling the other way will.