Tom Kivlehan took the action against the State broadcaster
RTÉ wants a Green Party member to pay its legal bill following his failed litigation over the exclusion of Eamon Ryan from its leaders' debates.
Tom Kivlehan, who unsuccessfully contested the election for the party, tried to argue that the criterion used by the broadcaster were unfair and unconstitutional.
Eamon Ryan was not invited to take part in any of the RTÉ leaders' debates because his party did not have at least three TDs in the outgoing Dáil.
This is a minimum requirement set down by the broadcaster, and one which Ms Justice Marie Baker ultimately ruled was not "unfair, irrational or disproportionate".
The legal action was brought by Tom Kivlehan, who failed to win a seat as a Green candidate in Dublin Mid-West.
Today, his barrister argued he should not have to pay costs because he brought the proceedings as a citizen who raised issues of exceptional public importance that go to the core of the democratic process.
RTÉ asked the court to look at how he initially presented himself as an "actively concerned" member of the Green Party.
Their side believes he was trying to gain a position of advantage and was not acting on behalf of a wider public interest.
A judgement on costs will be made tomorrow.