Almost 400 secondary schools across the country are closed today due to a strike by thousands of teachers.
The Teachers' Union of Ireland (TUI) says the strike is taking place because those hired after 2011 are paid at a lower rate than colleagues, despite doing the same work.
The action means hundreds of secondary schools whose teachers are mostly TUI members have had to close for health and safety reasons.
Today's strike will mainly impact schools run by the country's Education and Training Boards.
Around 19,000 members of the TUI are taking part in the action, which will also impact institutes of technology and centres of further / adult education.
TUI general secretary, John MacGabhann, explained that the strike is a last resort - suggesting the pay parity issue is now impacting on students.
He said: "The effect of the pay discrimination has been that there is now a significant and deepening crisis in teachers' supply... in the recruitment and retention of teachers.
"This has led - in a significant and growing number of schools - to a shortage of subject specialists, as a consequence of which subjects are being dropped."
One of the teachers demonstrating outside Greenhills Community College in Walkinstown this morning explained: "My colleagues that I'm working with, that have been working longer than me and they're doing the same work as I do... my wages are much less than theirs. So that's why I'm standing here today."
Meanwhile, the Association of Secondary Teachers in Ireland (ASTI) said a ballot of its member for industrial action is underway on the same issue.
The union is also holding a protest outside the Department of Education later in support of their TUI colleagues.