The millionaire businessman was trying to answer a question from host Claire Byre on the expenses of the Office of the President when a woman could be heard heckling from the audience.
At one point Mr Casey said that the “woman should not be in here” as the shouting continued.
The debate was then briefly adjourned with Ms Byrne saying they were going to a commercial break.
The woman was then removed from the building before the live debate continued after the impromptu break.
In a statement, RTÉ said: “Audience selection was founded on open applications from members of the public.
“The audience was selected by an external company to be representative both geographically, politically and demographically of the electorate.
“We regret a member of the audience decided to interrupt the candidates.
“They were removed from the studio and the live broadcast continued.”
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