Teachers' union Into has accused the Government of failing in its responsibility to young children by not reducing class sizes.
Labour Party education spokeswoman Jan O'Sullivan.
This follows the release of figures showing that more than one in four primary school students are being taught in classes of 30 or more.
The figures - which were contained in a written Dáil reply from Minister for Education Mary Hanafin to Labour Party education spokeswoman Jan O'Sullivan TD - also showed that the majority of primary schoolchildren are being taught in classes of 20 to 29.
Into General secretary John Carr said: "The situation is getting worse and it is our view this is a wake-up call to the Department of Education to do more and a wake-up call for parents to make this an issue in the next general election."
Mr Carr said: "When we lived in a poor country we were told class sizes would be reduced when resources permitted, now we are living in one of the richest countries in Europe and we still have a major problem with class sizes."
He said acknowledged that the current Minister for Education Mary Hanafin had put a lot of resources into children with special needs and children from disadvantaged areas.
"But we now have to look at the rest of the children in the classroom," he said on RTE's Morning Ireland programme.
"It is vital this Government reduces class sizes as quickly as possible. It is failing in its responsibility to young children in this country and our responsibility is to highlight that," he said.
He said his union plans to conduct a petition among parents to try to convince the Government "that class size is an important issue that has to be addressed".
