Almost 19,000 teachers are to strike today in a row over pay.
The action will mean hundreds of secondary schools, containing mostly Teachers Union of Ireland members, will have to close for health and safety reasons. College lecturers will also be striking.
In October, TUI members voted by a margin of 92% to 8% to engage in a campaign of industrial action, up to and including strike action. The Union announced in November that it would take strike action in February unless the matter was resolved.
The TUI says it is taking place because those hired after 2011 are paid at a lower rate than colleagues, despite doing the same work.
The union's General Secretary, John MacGabhann, says it is a last resort. He says the pay parity issue is now impacting on students;
"There is now a significant and deepening crisis in teacher supply, in the recruitment and retention of teachers. This has led, in a significant number and a growing number of schools, to a shortage of subject specialists."
Meanwhile the Association of Secondary Teachers in Ireland says a ballot of its member for industrial action is underway on the same issue.
The union is also holding a protest outside the Department later in support of their TUI colleagues.
