It said that it has "serious concern about the safety of teachers and students."
The Association of Secondary Teachers Ireland (ASTI) has directed its members to teach remotely, despite the Government stating Leaving Cert students should go into school three days per week.
ASTI, which is the country's second largest teachers' union, said that it was not consulted before this decision was made, and that it "poses a great threat to public health in the current context.
A statement released by the union reads: "The ASTI has not been provided with the necessary assurances that schools are sufficiently safe for students and teachers at this time, in the context of the new variant of Covid-19 circulating in the community and the alarmingly high numbers.
"ASTI Standing Committee decided to direct its members not to co-operate with the arrangements announced by the Minister for Education for in-school teaching, but to engage in remote teaching/ learning provision from Monday, 11 January. The decision is based on significant concerns about the health and safety of students, teachers and other staff."
Speaking after a meeting which confirmed this news, ASTI President Ann Piggott said: "The ASTI has repeatedly sought sufficient assurances that schools are safe for students and teachers at this time, in the context of the new variant of Covid-19 circulating in the community and the alarmingly high numbers.
"We engaged with the Department of Education and with public health officials today. Unfortunately, the assurances we sought have not been forthcoming."
This comes after the Government announced that Leaving Cert students will be asked to come into school three days a week,
while schools will be closed otherwise.
