The Teachers' Union of Ireland (TUI) says it may have to consider industrial action, unless the government deals with pay inequality.
The union is holding lunchtime protests about the issue at schools nationwide today.
It says there are real difficulties recruiting new teachers for second level subjects such as languages, maths and science.
According to the union, the current situation is likely to get 'much worse' ahead of the next school year - unless pay parity is restored for newly qualified teachers.
TUI President Joanne Irwin believes there's just one reason for the recruitment crisis.
She argued: "New teachers are not going into the profession. We have seen a 62% drop in the number of applicants going on to the teacher training programme.
"That's since 2011 - that's a direct result of the date on which teachers had a pay cut inflicted upon them."