Secretaries working in schools are staging a demonstration outside the Minister for Education's clinic in county Donegal and in other areas across the country.
Fórsa says their members are campaigning for fair pay and working conditions.
Fórsa balloted its members over the summer after education department officials refused to discuss proposals to overcome a two-tier pay system that leaves most earning just €12,500 a year.
They say the outcome of the vote will be revealed on Monday.
Joe O'Connor from Fórsa says the majority are employed by school management boards, which determine their pay and conditions.
"This is not a group that either the union or the group itself really wants to be in a situation where they have to take industrial action," said Mr O'Connor.
"It doesn't come naturally to school secretaries in any shape or form but we really feel like we have been boxed into a corner and that the time for a breakthrough on this issue is really long overdue."
He added that irregular and short-term contracts force some school secretaries to sign on during the summer holidays and other school breaks.
"We think this is a totally unacceptable situation for a really invaluable member of our school community.
"Our campaign that was launched in January #SupportOurSecretaries has received huge public and political support and really now we need the Department to catch up with the view of anyone that we have come to about this issue which is that school secretaries deserve to be treated with respect and treated fairly."
Mr O'Connor said that 90% of school secretaries in Ireland have no access to occupational pensions and in most cases have no sick pay or holiday pay.
