The INTO says pay inequality is the real reason for teacher shortages, not career breaks.
It is after reports that schools will be told to clamp down on leave to solve the problem.
Teachers are entitled to a career break once they are made permanent, with their job secured for when they return.
President of the INTO John Boyle says many people need breaks for personal reasons and curbing them is not the solution.
He said: "The career break scheme is not only used for people going abroad.
"I do accept that more teachers at the moment are going abroad but because of this issue with pay and equality and not being able to get the deposit for a house but that is something that can easily be solved.
Schools are set to limit career breaks for teachers to tackle staff shortages.
This year, over 1,700 primary teachers and 557 secondary teachers are on leave.
According to the Irish Independent, the Government is considering a range of measures to deal with the problem.
President of the Irish National Teachers Organisation (INTO) John Boyle says a lot of teachers leave because of pay inequality.
He said: "A lot of young teachers lost in the region of €50,000 deposit for a house.
"So in that situation, it is much easier to go abroad when you go abroad get tax free salaries and return after a few years.
"We have also had a continuation of the baby boom, it is actually only peaking now."