The council says the charge has been payable since 2009, and anyone who hasn't paid since then now owes just over €4,000.
However, from September, that will rise substantially.
The combined principal charge and late penalty fees for the years 2009 to 2013 is now €4,220, and that is set to rise to €7,230 from the 1st of September.
With that in mind, the council says all property owners who have yet to register and pay their NPPR liability should do so before the 31st August.
The council says it is actively identifying property owners who may have a NPPR liability using data provided by the Revenue Commissioners, and will be pursuing these outstanding charges.
The authority is also carrying out another publicity campaign north of the border, where the owners of a substantial number of Donegal holiday homes are based.