The Association of Secondary Teachers in Ireland is to ballot its members for industrial action over a range of school reopening issues.
The union's Central Executive Committee took the decision following a meeting today.
Among the issues of concern are physical distancing in schools, provision of PPE, definition of close contacts as well as testing and the turnaround times for those tests.
There is also concern over the provisions that are being made for high-risk staff members.
The ASTI said IT resources for students and teachers to facilitate remote teaching and learning is also a matter of concern.
Association President Ann Piggott said that it was "unacceptable" that high risk teachers were being asked to work in "crowded" classrooms, adding that the "safety of students and their teachers must be the priority".
Ms Piggott said teachers are reporting that new work practices are being implemented without any consultation with school staff.
"It is unthinkable that at a time when teachers have demonstrated tremendous commitment to their students and to keeping education going, that schools would introduce work changes which have a further negative impact on teachers' working lives. This smacks of crisis opportunism and cannot go unchallenged."
The ballot of ASTI members will also deal with the issue of returning teachers who are "being forced to work precarious contracts and those enduring unequal pay" the union said.
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It is not known yet what wording will be on the ballot paper or exactly when the result will be known.
However, the process is expected to take several weeks.
Sinn Féin spokesperson on Education Donnchadh Ó Laoghaire said the issues identified by the ASTI have "been on the agenda for weeks now".
"It is unacceptable that the Department of Education has allowed things to get to this point; with the ASTI now seeing no alternative but to ballot their members for industrial action," he said.