Catherine Murphy and Róisín Shortall have criticised reasons given by organisers
The co-leaders of the Social Democrats have said they will withdraw from their panels at the MacGill Summer School due to the gender-balance on them.
They are calling for significant changes to be made across all sessions.
Catherine Murphy and Róisín Shortall accepted a place on panels, but said they were not aware the programme for other sessions was predominantly male.
Of 56 speakers listed to talk at this year's event, 12 of them are women - including Deputies Murphy and Shortall.
Both leaders said they were "surprised" by the organisers claim that it was hard to find people with the right aptitude.
Deputy Murphy said: "I find the comment from the organisers about it being 'difficult to find people with the right aptitude' quite offensive when the implication is obviously that that is the reason more women are not invited to speak at the event.
The assertion from @MacGillSummerSc that it's difficult to find people with the right aptitude is offensive to women says @CathMurphyTD - who has been invited to discuss dysfunctionality in Ireland - women must be part of discussions and solutions #MacGill2018 #NoCountryForWomen pic.twitter.com/cNtqlO6QCK— Social Democrats (@SocDems) June 20, 2018
"That is simply not true or else the organisers have conducted a very limited search.
"There is an abundance of articulate and well-informed women that could have been approached to participate and weren't.
"I cannot in good conscience take part in an event that has so blatantly disregarded the importance of equal female participation and for that reason I will withdraw from the session I was due to speak at unless significant changes are made across the programme."
Deputy Shortall added: "Irish politics has come a long way from the male pale and stale boys club that it traditionally was. High-profile events like MacGill have a responsibility to reflect that change but also to recognise the wealth of fantastic and informed female voices across the Irish public life."
The MacGill Summer School was founded in 1981 in Glenties, Co Donegal.
The school debates and contributes to public policy - ranging across economic, social and political and public service reform.
Among speakers listed this year are Bertie Ahern, Pat Cox, Stephen Donnelly, Professor Brigid Laffan, Micheál Martin, Mairead McGuinness, David Quinn and Vicky Phelan.