An Post is seeking summary judgment against Spanish postal operator Correos to recover money it is allegedly owed.
The semi-state company has made the application through the High Court, which is the first step in the recovery of a debt. It is understood the issue relates to so-called terminal dues and the figure in question is allegedly around €500,000.
When a postal operator in one country sends an item of post to another country, it remunerates the operator in the destination country for processing and delivering the item.
This system of remuneration is known as terminal dues. Nothing has been served on Correos at this point.
A spokeswoman for An Post declined to comment. A spokeswoman for Correos said An Post and Correos have signed a series of international agreements explaining in detail the prices and costs between the two companies, which it said "Correos is fulfilling".
"We are not aware of any legal claims regarding this," the spokeswoman said. "Correos has attempted to contact An Post numerous times... to come to an agreement and define further actions but it has not been possible."