Members of the Association of Secondary Teachers Ireland (ASTI) have today voted to reject the latest public-service pay deal.
The vote comes amid concerns over its failure to address the issue of lower pay for staff recruited since 2010.
Some 51.5% of those who voted rejected the Public Service Stability Agreement (PSSA) 2018-2020, while 48.5% were in favour.
The turnout was 64%.
ASTI president Ger Curtin said by rejecting the agreement, members continue to stand up for their most vulnerable colleagues.
"We will not stop until the discriminatory treatment of post 2010 teachers is put to an end," he said.
"While some progress has been achieved on the issue, an unacceptable gap remains.
"Teachers who are five and six years teaching have already lost out significantly in terms of their pay. The effects of this can be seen on teacher recruitment.
"The discriminatory treatment of post 2010 teachers has serious implications for the future of the teaching profession and the education of children and young people."