Revenue is to give businesses and agents more time to move to its new customs declaration system.
Last month Revenue launched its new Automated Import System (AIS), which is set to replace its Automated Entry Processing (AEP) system for goods being imported.
In order to give businesses and customs agents time to switch, it has been running both systems in parallel since the 23 November.
That dual system was due to end on Tuesday, however Revenue says it will now continue until the end of March 2021.
Revenue said its new AIS has gotten "excellent engagement", with 130 customs agents and businesses actively using it - including 47 of the top 50 firms filing import declarations.
However there had been concerns that Covid-19 and Brexit would make it more difficult for others to make the move.
Revenue said it recognised the very challenging business environment, and has decided to extend the deadline for the end of the AEP system as a result.
It encouraged firms that had not already done so to begin the process of moving to AIS, which it said was a key part of being prepared for Brexit.
The system complies with European Union requirements around customs codes, which is something many more firms will have to use once the UK leaves the customs union.